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 $189.38   4.190%   $197.315   $197.32   $197.30   $197.30  
  Purchase #2 $133.89   4.540%   $139.9686   $139.97   $139.95   $140.00  
  Purchase #3 $66.37   13.852%   $75.5636   $75.56   $75.55   $75.60  
  Purchase #4 $119.94   13.385%   $135.994   $135.99   $136.00   $136.00  
  Purchase #5 $178.79   9.476%   $195.7321   $195.73   $195.75   $195.70  
  Purchase #6 $206.65   4.151%   $215.228   $215.23   $215.25   $215.20  
  Purchase #7 $149.51   11.165%   $166.2028   $166.20   $166.20   $166.20  
  7 purchase totals = $1,044.53       $1,126.0041   $1,126.00   $1,126.00   $1,126.00