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 $223.39   10.572%   $247.0068   $247.01   $247.00   $247.00  
  Purchase #2 $125.90   10.608%   $139.2555   $139.26   $139.25   $139.30  
  Purchase #3 $194.28   3.342%   $200.7728   $200.77   $200.75   $200.80  
  Purchase #4 $117.85   6.389%   $125.3794   $125.38   $125.40   $125.40  
  Purchase #5 $46.29   3.261%   $47.7995   $47.80   $47.80   $47.80  
  Purchase #6 $32.25   10.418%   $35.6098   $35.61   $35.60   $35.60  
  Purchase #7 $138.72   12.313%   $155.8006   $155.80   $155.80   $155.80  
  7 purchase totals = $878.68       $951.6244   $951.63   $951.60   $951.70