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 $175.58   10.687%   $194.3442   $194.34   $194.35   $194.30  
  Purchase #2 $95.82   6.849%   $102.3827   $102.38   $102.40   $102.40  
  Purchase #3 $108.58   11.603%   $121.1785   $121.18   $121.20   $121.20  
  Purchase #4 $204.44   11.484%   $227.9179   $227.92   $227.90   $227.90  
  Purchase #5 $88.88   13.849%   $101.189   $101.19   $101.20   $101.20  
  Purchase #6 $157.65   12.204%   $176.8896   $176.89   $176.90   $176.90  
  Purchase #7 $117.84   12.555%   $132.6348   $132.63   $132.65   $132.60  
  7 purchase totals = $948.79       $1,056.5367   $1,056.53   $1,056.60   $1,056.50