Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $85.49   13.498%   $97.0294   $97.03   $97.05   $97.00  
  Purchase #2 $17.34   5.713%   $18.3306   $18.33   $18.35   $18.30  
  Purchase #3 $250.52   5.301%   $263.8001   $263.80   $263.80   $263.80  
  Purchase #4 $87.36   13.850%   $99.4594   $99.46   $99.45   $99.50  
  Purchase #5 $236.28   11.192%   $262.7245   $262.72   $262.70   $262.70  
  Purchase #6 $226.94   7.394%   $243.7199   $243.72   $243.70   $243.70  
  Purchase #7 $216.59   4.409%   $226.1395   $226.14   $226.15   $226.10  
  7 purchase totals = $1,120.52       $1,211.2034   $1,211.20   $1,211.20   $1,211.10