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 $52.68   12.352%   $59.187   $59.19   $59.20   $59.20  
  Purchase #2 $85.75   10.728%   $94.9493   $94.95   $94.95   $94.90  
  Purchase #3 $129.37   9.528%   $141.6964   $141.70   $141.70   $141.70  
  Purchase #4 $131.45   8.222%   $142.2578   $142.26   $142.25   $142.30  
  Purchase #5 $138.67   12.290%   $155.7125   $155.71   $155.70   $155.70  
  Purchase #6 $229.25   9.157%   $250.2424   $250.24   $250.25   $250.20  
  Purchase #7 $117.94   7.103%   $126.3173   $126.32   $126.30   $126.30  
  7 purchase totals = $885.11       $970.3627   $970.37   $970.35   $970.30