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 $70.53   8.116%   $76.2542   $76.25   $76.25   $76.30  
  Purchase #2 $196.47   3.146%   $202.6509   $202.65   $202.65   $202.70  
  Purchase #3 $21.40   13.189%   $24.2224   $24.22   $24.20   $24.20  
  Purchase #4 $45.52   9.714%   $49.9418   $49.94   $49.95   $49.90  
  Purchase #5 $78.84   6.498%   $83.963   $83.96   $83.95   $84.00  
  Purchase #6 $185.71   11.417%   $206.9125   $206.91   $206.90   $206.90  
  Purchase #7 $14.53   4.808%   $15.2286   $15.23   $15.25   $15.20  
  7 purchase totals = $613.00       $659.1734   $659.16   $659.15   $659.20