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 $63.62   5.854%   $67.3443   $67.34   $67.35   $67.30  
  Purchase #2 $197.89   3.535%   $204.8854   $204.89   $204.90   $204.90  
  Purchase #3 $72.67   7.680%   $78.2511   $78.25   $78.25   $78.30  
  Purchase #4 $67.92   11.791%   $75.9284   $75.93   $75.95   $75.90  
  Purchase #5 $162.27   4.612%   $169.7539   $169.75   $169.75   $169.80  
  Purchase #6 $227.51   3.205%   $234.8017   $234.80   $234.80   $234.80  
  Purchase #7 $31.67   8.362%   $34.3182   $34.32   $34.30   $34.30  
  7 purchase totals = $823.55       $865.2830   $865.28   $865.30   $865.30