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 $53.52   9.333%   $58.515   $58.52   $58.50   $58.50  
  Purchase #2 $70.27   3.350%   $72.624   $72.62   $72.60   $72.60  
  Purchase #3 $61.65   7.801%   $66.4593   $66.46   $66.45   $66.50  
  Purchase #4 $234.68   6.335%   $249.547   $249.55   $249.55   $249.50  
  Purchase #5 $6.75   8.653%   $7.3341   $7.33   $7.35   $7.30  
  Purchase #6 $130.44   7.746%   $140.5439   $140.54   $140.55   $140.50  
  Purchase #7 $208.63   8.426%   $226.2092   $226.21   $226.20   $226.20  
  7 purchase totals = $765.94       $821.2325   $821.23   $821.20   $821.10