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 $92.85   12.612%   $104.5602   $104.56   $104.55   $104.60  
  Purchase #2 $46.98   6.662%   $50.1098   $50.11   $50.10   $50.10  
  Purchase #3 $187.53   11.506%   $209.1072   $209.11   $209.10   $209.10  
  Purchase #4 $43.41   5.360%   $45.7368   $45.74   $45.75   $45.70  
  Purchase #5 $213.29   9.758%   $234.1028   $234.10   $234.10   $234.10  
  Purchase #6 $76.60   9.343%   $83.7567   $83.76   $83.75   $83.80  
  Purchase #7 $247.49   10.785%   $274.1818   $274.18   $274.20   $274.20  
  7 purchase totals = $908.15       $1,001.5553   $1,001.56   $1,001.55   $1,001.60