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 $83.42   13.321%   $94.5324   $94.53   $94.55   $94.50  
  Purchase #2 $48.48   8.762%   $52.7278   $52.73   $52.75   $52.70  
  Purchase #3 $160.28   13.541%   $181.9835   $181.98   $182.00   $182.00  
  Purchase #4 $56.56   9.359%   $61.8535   $61.85   $61.85   $61.90  
  Purchase #5 $190.93   3.192%   $197.0245   $197.02   $197.00   $197.00  
  Purchase #6 $161.85   9.688%   $177.53   $177.53   $177.55   $177.50  
  Purchase #7 $50.90   6.377%   $54.1459   $54.15   $54.15   $54.10  
  7 purchase totals = $752.42       $819.7976   $819.79   $819.85   $819.70