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 $66.84   10.328%   $73.7432   $73.74   $73.75   $73.70  
  Purchase #2 $241.37   11.217%   $268.4445   $268.44   $268.45   $268.40  
  Purchase #3 $146.68   6.812%   $156.6718   $156.67   $156.65   $156.70  
  Purchase #4 $231.28   7.797%   $249.3129   $249.31   $249.30   $249.30  
  Purchase #5 $201.42   7.296%   $216.1156   $216.12   $216.10   $216.10  
  Purchase #6 $113.51   5.282%   $119.5056   $119.51   $119.50   $119.50  
  Purchase #7 $101.97   11.496%   $113.6925   $113.69   $113.70   $113.70  
  7 purchase totals = $1,103.07       $1,197.4861   $1,197.48   $1,197.45   $1,197.40