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 $53.86   6.618%   $57.4245   $57.42   $57.40   $57.40  
  Purchase #2 $112.64   11.287%   $125.3537   $125.35   $125.35   $125.40  
  Purchase #3 $57.30   11.281%   $63.764   $63.76   $63.75   $63.80  
  Purchase #4 $184.64   3.451%   $191.0119   $191.01   $191.00   $191.00  
  Purchase #5 $223.42   12.555%   $251.4704   $251.47   $251.45   $251.50  
  Purchase #6 $88.44   12.491%   $99.487   $99.49   $99.50   $99.50  
  Purchase #7 $158.50   12.843%   $178.8562   $178.86   $178.85   $178.90  
  7 purchase totals = $878.80       $967.3677   $967.36   $967.30   $967.50