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 $205.96   13.275%   $233.3012   $233.30   $233.30   $233.30  
  Purchase #2 $22.47   6.594%   $23.9517   $23.95   $23.95   $24.00  
  Purchase #3 $133.55   9.417%   $146.1264   $146.13   $146.15   $146.10  
  Purchase #4 $209.37   7.472%   $225.0141   $225.01   $225.00   $225.00  
  Purchase #5 $226.36   8.361%   $245.286   $245.29   $245.30   $245.30  
  Purchase #6 $29.76   5.451%   $31.3822   $31.38   $31.40   $31.40  
  Purchase #7 $104.93   5.461%   $110.6602   $110.66   $110.65   $110.70  
  7 purchase totals = $932.40       $1,015.7218   $1,015.72   $1,015.75   $1,015.80