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 $176.86   11.819%   $197.7631   $197.76   $197.75   $197.80  
  Purchase #2 $91.60   3.674%   $94.9654   $94.97   $94.95   $95.00  
  Purchase #3 $99.71   7.576%   $107.264   $107.26   $107.25   $107.30  
  Purchase #4 $164.72   11.565%   $183.7699   $183.77   $183.75   $183.80  
  Purchase #5 $126.69   10.638%   $140.1673   $140.17   $140.15   $140.20  
  Purchase #6 $30.84   8.263%   $33.3883   $33.39   $33.40   $33.40  
  Purchase #7 $169.40   8.706%   $184.148   $184.15   $184.15   $184.10  
  7 purchase totals = $859.82       $941.4660   $941.47   $941.40   $941.60