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 $58.87   10.833%   $65.2474   $65.25   $65.25   $65.20  
  Purchase #2 $142.76   8.719%   $155.2072   $155.21   $155.20   $155.20  
  Purchase #3 $29.74   11.340%   $33.1125   $33.11   $33.10   $33.10  
  Purchase #4 $213.73   7.240%   $229.2041   $229.20   $229.20   $229.20  
  Purchase #5 $43.55   11.108%   $48.3875   $48.39   $48.40   $48.40  
  Purchase #6 $180.28   4.442%   $188.288   $188.29   $188.30   $188.30  
  Purchase #7 $13.94   12.343%   $15.6606   $15.66   $15.65   $15.70  
  7 purchase totals = $682.87       $735.1073   $735.11   $735.10   $735.10