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 $117.44   13.671%   $133.4952   $133.50   $133.50   $133.50  
  Purchase #2 $200.87   9.409%   $219.7699   $219.77   $219.75   $219.80  
  Purchase #3 $245.92   5.429%   $259.271   $259.27   $259.25   $259.30  
  Purchase #4 $55.84   6.200%   $59.3021   $59.30   $59.30   $59.30  
  Purchase #5 $245.87   9.377%   $268.9252   $268.93   $268.95   $268.90  
  Purchase #6 $200.27   9.746%   $219.7883   $219.79   $219.80   $219.80  
  Purchase #7 $119.42   5.474%   $125.9571   $125.96   $125.95   $126.00  
  7 purchase totals = $1,185.63       $1,286.5088   $1,286.52   $1,286.50   $1,286.60