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 $118.66   4.674%   $124.2062   $124.21   $124.20   $124.20  
  Purchase #2 $118.89   4.635%   $124.4006   $124.40   $124.40   $124.40  
  Purchase #3 $180.94   7.297%   $194.1432   $194.14   $194.15   $194.10  
  Purchase #4 $86.75   9.755%   $95.2125   $95.21   $95.20   $95.20  
  Purchase #5 $119.50   10.812%   $132.4203   $132.42   $132.40   $132.40  
  Purchase #6 $44.97   7.821%   $48.4871   $48.49   $48.50   $48.50  
  Purchase #7 $88.66   11.271%   $98.6529   $98.65   $98.65   $98.70  
  7 purchase totals = $758.37       $817.5228   $817.52   $817.50   $817.50