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 $224.97   9.389%   $246.0924   $246.09   $246.10   $246.10  
  Purchase #2 $131.35   11.398%   $146.3213   $146.32   $146.30   $146.30  
  Purchase #3 $169.31   7.808%   $182.5297   $182.53   $182.55   $182.50  
  Purchase #4 $41.29   7.738%   $44.485   $44.49   $44.50   $44.50  
  Purchase #5 $229.38   10.682%   $253.8824   $253.88   $253.90   $253.90  
  Purchase #6 $111.80   4.557%   $116.8947   $116.89   $116.90   $116.90  
  Purchase #7 $241.99   6.358%   $257.3757   $257.38   $257.40   $257.40  
  7 purchase totals = $1,150.09       $1,247.5812   $1,247.58   $1,247.65   $1,247.60