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 $183.36   10.675%   $202.9337   $202.93   $202.95   $202.90  
  Purchase #2 $57.85   11.868%   $64.7156   $64.72   $64.70   $64.70  
  Purchase #3 $104.77   7.794%   $112.9358   $112.94   $112.95   $112.90  
  Purchase #4 $69.32   4.738%   $72.6044   $72.60   $72.60   $72.60  
  Purchase #5 $249.81   5.536%   $263.6395   $263.64   $263.65   $263.60  
  Purchase #6 $7.70   7.624%   $8.287   $8.29   $8.30   $8.30  
  Purchase #7 $188.61   11.186%   $209.7079   $209.71   $209.70   $209.70  
  7 purchase totals = $861.42       $934.8239   $934.83   $934.85   $934.70