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 $63.43   12.758%   $71.5224   $71.52   $71.50   $71.50  
  Purchase #2 $107.41   11.696%   $119.9727   $119.97   $119.95   $120.00  
  Purchase #3 $34.73   9.733%   $38.1103   $38.11   $38.10   $38.10  
  Purchase #4 $229.36   9.568%   $251.3052   $251.31   $251.30   $251.30  
  Purchase #5 $225.36   9.602%   $246.9991   $247.00   $247.00   $247.00  
  Purchase #6 $72.29   13.349%   $81.94   $81.94   $81.95   $81.90  
  Purchase #7 $198.76   4.133%   $206.9748   $206.97   $206.95   $207.00  
  7 purchase totals = $931.34       $1,016.8245   $1,016.82   $1,016.75   $1,016.80