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 $106.43   12.268%   $119.4868   $119.49   $119.50   $119.50  
  Purchase #2 $29.41   9.648%   $32.2475   $32.25   $32.25   $32.20  
  Purchase #3 $124.64   9.571%   $136.5693   $136.57   $136.55   $136.60  
  Purchase #4 $213.51   7.341%   $229.1838   $229.18   $229.20   $229.20  
  Purchase #5 $173.74   5.846%   $183.8968   $183.90   $183.90   $183.90  
  Purchase #6 $187.94   3.842%   $195.1607   $195.16   $195.15   $195.20  
  Purchase #7 $114.31   9.712%   $125.4118   $125.41   $125.40   $125.40  
  7 purchase totals = $949.98       $1,021.9567   $1,021.96   $1,021.95   $1,022.00