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 $59.96   13.790%   $68.2285   $68.23   $68.25   $68.20  
  Purchase #2 $240.86   13.331%   $272.969   $272.97   $272.95   $273.00  
  Purchase #3 $107.75   9.417%   $117.8968   $117.90   $117.90   $117.90  
  Purchase #4 $23.97   6.146%   $25.4432   $25.44   $25.45   $25.40  
  Purchase #5 $234.43   11.810%   $262.1162   $262.12   $262.10   $262.10  
  Purchase #6 $66.70   3.238%   $68.8597   $68.86   $68.85   $68.90  
  Purchase #7 $234.91   6.321%   $249.7587   $249.76   $249.75   $249.80  
  7 purchase totals = $968.58       $1,065.2721   $1,065.28   $1,065.25   $1,065.30