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 $111.89   12.191%   $125.5305   $125.53   $125.55   $125.50  
  Purchase #2 $249.31   9.273%   $272.4285   $272.43   $272.45   $272.40  
  Purchase #3 $93.78   9.750%   $102.9236   $102.92   $102.90   $102.90  
  Purchase #4 $158.64   5.299%   $167.0463   $167.05   $167.05   $167.00  
  Purchase #5 $48.63   5.633%   $51.3693   $51.37   $51.35   $51.40  
  Purchase #6 $79.55   6.733%   $84.9061   $84.91   $84.90   $84.90  
  Purchase #7 $235.96   4.428%   $246.4083   $246.41   $246.40   $246.40  
  7 purchase totals = $977.76       $1,050.6126   $1,050.62   $1,050.60   $1,050.50