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 $151.89   11.528%   $169.3999   $169.40   $169.40   $169.40  
  Purchase #2 $154.34   13.610%   $175.3457   $175.35   $175.35   $175.30  
  Purchase #3 $13.82   11.133%   $15.3586   $15.36   $15.35   $15.40  
  Purchase #4 $66.29   3.529%   $68.6294   $68.63   $68.65   $68.60  
  Purchase #5 $227.99   12.112%   $255.6041   $255.60   $255.60   $255.60  
  Purchase #6 $126.87   10.858%   $140.6455   $140.65   $140.65   $140.60  
  Purchase #7 $110.42   13.445%   $125.266   $125.27   $125.25   $125.30  
  7 purchase totals = $851.62       $950.2492   $950.26   $950.25   $950.20