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 $36.61   12.282%   $41.1064   $41.11   $41.10   $41.10  
  Purchase #2 $162.79   8.563%   $176.7297   $176.73   $176.75   $176.70  
  Purchase #3 $48.48   12.419%   $54.5007   $54.50   $54.50   $54.50  
  Purchase #4 $58.67   6.503%   $62.4853   $62.49   $62.50   $62.50  
  Purchase #5 $185.29   9.128%   $202.2033   $202.20   $202.20   $202.20  
  Purchase #6 $170.46   8.394%   $184.7684   $184.77   $184.75   $184.80  
  Purchase #7 $146.39   7.549%   $157.441   $157.44   $157.45   $157.40  
  7 purchase totals = $808.69       $879.2348   $879.24   $879.25   $879.20