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 $239.83   11.834%   $268.2115   $268.21   $268.20   $268.20  
  Purchase #2 $80.54   13.341%   $91.2848   $91.28   $91.30   $91.30  
  Purchase #3 $58.29   11.703%   $65.1117   $65.11   $65.10   $65.10  
  Purchase #4 $44.85   9.684%   $49.1933   $49.19   $49.20   $49.20  
  Purchase #5 $140.46   5.630%   $148.3679   $148.37   $148.35   $148.40  
  Purchase #6 $223.83   8.196%   $242.1751   $242.18   $242.20   $242.20  
  Purchase #7 $89.29   10.767%   $98.9039   $98.90   $98.90   $98.90  
  7 purchase totals = $877.09       $963.2482   $963.24   $963.25   $963.30