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 $240.83   11.237%   $267.8921   $267.89   $267.90   $267.90  
  Purchase #2 $226.81   13.738%   $257.9692   $257.97   $257.95   $258.00  
  Purchase #3 $117.73   3.766%   $122.1637   $122.16   $122.15   $122.20  
  Purchase #4 $34.81   7.804%   $37.5266   $37.53   $37.55   $37.50  
  Purchase #5 $192.39   6.562%   $205.0146   $205.01   $205.00   $205.00  
  Purchase #6 $124.63   6.639%   $132.9042   $132.90   $132.90   $132.90  
  Purchase #7 $232.38   3.851%   $241.329   $241.33   $241.35   $241.30  
  7 purchase totals = $1,169.58       $1,264.7994   $1,264.79   $1,264.80   $1,264.80