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 $54.78   11.202%   $60.9165   $60.92   $60.90   $60.90  
  Purchase #2 $122.48   10.208%   $134.9828   $134.98   $135.00   $135.00  
  Purchase #3 $30.56   9.390%   $33.4296   $33.43   $33.45   $33.40  
  Purchase #4 $220.82   10.145%   $243.2222   $243.22   $243.20   $243.20  
  Purchase #5 $93.74   8.500%   $101.7079   $101.71   $101.70   $101.70  
  Purchase #6 $207.58   9.484%   $227.2669   $227.27   $227.25   $227.30  
  Purchase #7 $135.30   13.344%   $153.3544   $153.35   $153.35   $153.40  
  7 purchase totals = $865.26       $954.8803   $954.88   $954.85   $954.90