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 $54.72   10.674%   $60.5608   $60.56   $60.55   $60.60  
  Purchase #2 $39.44   13.289%   $44.6812   $44.68   $44.70   $44.70  
  Purchase #3 $174.89   11.224%   $194.5197   $194.52   $194.50   $194.50  
  Purchase #4 $139.71   5.379%   $147.225   $147.23   $147.25   $147.20  
  Purchase #5 $231.94   6.767%   $247.6354   $247.64   $247.65   $247.60  
  Purchase #6 $91.89   5.719%   $97.1452   $97.15   $97.15   $97.10  
  Purchase #7 $86.93   10.781%   $96.3019   $96.30   $96.30   $96.30  
  7 purchase totals = $819.52       $888.0692   $888.08   $888.10   $888.00