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 $59.38   7.545%   $63.8602   $63.86   $63.85   $63.90  
  Purchase #2 $117.44   3.791%   $121.8922   $121.89   $121.90   $121.90  
  Purchase #3 $219.97   6.151%   $233.5004   $233.50   $233.50   $233.50  
  Purchase #4 $23.68   11.134%   $26.3165   $26.32   $26.30   $26.30  
  Purchase #5 $168.62   9.390%   $184.4534   $184.45   $184.45   $184.50  
  Purchase #6 $27.42   6.738%   $29.2676   $29.27   $29.25   $29.30  
  Purchase #7 $154.62   8.122%   $167.1782   $167.18   $167.20   $167.20  
  7 purchase totals = $771.13       $826.4685   $826.47   $826.45   $826.60