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 $217.39   12.228%   $243.9724   $243.97   $243.95   $244.00  
  Purchase #2 $183.61   6.722%   $195.9523   $195.95   $195.95   $196.00  
  Purchase #3 $86.95   10.754%   $96.3006   $96.30   $96.30   $96.30  
  Purchase #4 $86.78   12.404%   $97.5442   $97.54   $97.55   $97.50  
  Purchase #5 $145.72   5.163%   $153.2435   $153.24   $153.25   $153.20  
  Purchase #6 $47.85   9.781%   $52.5302   $52.53   $52.55   $52.50  
  Purchase #7 $99.99   9.340%   $109.3291   $109.33   $109.35   $109.30  
  7 purchase totals = $868.29       $948.8723   $948.86   $948.90   $948.80