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 $68.53   11.609%   $76.4856   $76.49   $76.50   $76.50  
  Purchase #2 $44.68   13.263%   $50.6059   $50.61   $50.60   $50.60  
  Purchase #3 $71.44   4.760%   $74.8405   $74.84   $74.85   $74.80  
  Purchase #4 $30.76   7.241%   $32.9873   $32.99   $33.00   $33.00  
  Purchase #5 $203.64   8.462%   $220.872   $220.87   $220.85   $220.90  
  Purchase #6 $184.92   5.263%   $194.6523   $194.65   $194.65   $194.70  
  Purchase #7 $221.50   13.376%   $251.1278   $251.13   $251.15   $251.10  
  7 purchase totals = $825.47       $901.5714   $901.58   $901.60   $901.60