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 $84.66   10.641%   $93.6687   $93.67   $93.65   $93.70  
  Purchase #2 $13.27   6.625%   $14.1491   $14.15   $14.15   $14.10  
  Purchase #3 $104.53   13.306%   $118.4388   $118.44   $118.45   $118.40  
  Purchase #4 $86.37   3.471%   $89.3679   $89.37   $89.35   $89.40  
  Purchase #5 $135.96   9.152%   $148.4031   $148.40   $148.40   $148.40  
  Purchase #6 $195.85   5.549%   $206.7177   $206.72   $206.70   $206.70  
  Purchase #7 $110.93   11.485%   $123.6703   $123.67   $123.65   $123.70  
  7 purchase totals = $731.57       $794.4156   $794.42   $794.35   $794.40