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 $215.38   12.485%   $242.2702   $242.27   $242.25   $242.30  
  Purchase #2 $118.79   5.241%   $125.0158   $125.02   $125.00   $125.00  
  Purchase #3 $56.95   4.450%   $59.4843   $59.48   $59.50   $59.50  
  Purchase #4 $67.31   9.437%   $73.662   $73.66   $73.65   $73.70  
  Purchase #5 $95.85   5.713%   $101.3259   $101.33   $101.35   $101.30  
  Purchase #6 $133.26   3.267%   $137.6136   $137.61   $137.60   $137.60  
  Purchase #7 $247.26   9.270%   $270.181   $270.18   $270.20   $270.20  
  7 purchase totals = $934.80       $1,009.5528   $1,009.55   $1,009.55   $1,009.60