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 $42.57   8.657%   $46.2553   $46.26   $46.25   $46.30  
  Purchase #2 $107.87   9.431%   $118.0432   $118.04   $118.05   $118.00  
  Purchase #3 $112.38   6.176%   $119.3206   $119.32   $119.30   $119.30  
  Purchase #4 $214.65   3.305%   $221.7442   $221.74   $221.75   $221.70  
  Purchase #5 $205.62   12.429%   $231.1765   $231.18   $231.20   $231.20  
  Purchase #6 $141.80   5.326%   $149.3523   $149.35   $149.35   $149.40  
  Purchase #7 $88.49   8.578%   $96.0807   $96.08   $96.10   $96.10  
  7 purchase totals = $913.38       $981.9728   $981.97   $982.00   $982.00