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 $87.55   5.318%   $92.2059   $92.21   $92.20   $92.20  
  Purchase #2 $165.63   8.276%   $179.3375   $179.34   $179.35   $179.30  
  Purchase #3 $146.66   13.837%   $166.9533   $166.95   $166.95   $167.00  
  Purchase #4 $247.61   11.176%   $275.2829   $275.28   $275.30   $275.30  
  Purchase #5 $231.64   13.273%   $262.3856   $262.39   $262.40   $262.40  
  Purchase #6 $235.98   5.546%   $249.0675   $249.07   $249.05   $249.10  
  Purchase #7 $18.85   9.628%   $20.6649   $20.66   $20.65   $20.70  
  7 purchase totals = $1,133.92       $1,245.8976   $1,245.90   $1,245.90   $1,246.00