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 $191.83   6.217%   $203.7561   $203.76   $203.75   $203.80  
  Purchase #2 $148.40   6.696%   $158.3369   $158.34   $158.35   $158.30  
  Purchase #3 $236.99   9.245%   $258.8997   $258.90   $258.90   $258.90  
  Purchase #4 $170.72   5.748%   $180.533   $180.53   $180.55   $180.50  
  Purchase #5 $195.26   7.469%   $209.844   $209.84   $209.85   $209.80  
  Purchase #6 $60.69   5.837%   $64.2325   $64.23   $64.25   $64.20  
  Purchase #7 $197.91   6.376%   $210.5287   $210.53   $210.55   $210.50  
  7 purchase totals = $1,201.80       $1,286.1309   $1,286.13   $1,286.20   $1,286.00