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 $54.39   10.556%   $60.1314   $60.13   $60.15   $60.10  
  Purchase #2 $228.41   11.695%   $255.1225   $255.12   $255.10   $255.10  
  Purchase #3 $132.97   11.733%   $148.5714   $148.57   $148.55   $148.60  
  Purchase #4 $155.98   8.499%   $169.2367   $169.24   $169.25   $169.20  
  Purchase #5 $180.25   10.436%   $199.0609   $199.06   $199.05   $199.10  
  Purchase #6 $214.49   5.120%   $225.4719   $225.47   $225.45   $225.50  
  Purchase #7 $44.92   13.419%   $50.9478   $50.95   $50.95   $50.90  
  7 purchase totals = $1,011.41       $1,108.5426   $1,108.54   $1,108.50   $1,108.50