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 $218.64   12.563%   $246.1077   $246.11   $246.10   $246.10  
  Purchase #2 $152.42   11.321%   $169.6755   $169.68   $169.70   $169.70  
  Purchase #3 $26.90   12.309%   $30.2111   $30.21   $30.20   $30.20  
  Purchase #4 $91.82   11.328%   $102.2214   $102.22   $102.20   $102.20  
  Purchase #5 $167.95   8.687%   $182.5398   $182.54   $182.55   $182.50  
  Purchase #6 $67.73   6.441%   $72.0925   $72.09   $72.10   $72.10  
  Purchase #7 $226.95   9.843%   $249.2887   $249.29   $249.30   $249.30  
  7 purchase totals = $952.41       $1,052.1367   $1,052.14   $1,052.15   $1,052.10