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 $213.74   11.591%   $238.5146   $238.51   $238.50   $238.50  
  Purchase #2 $141.97   6.223%   $150.8048   $150.80   $150.80   $150.80  
  Purchase #3 $99.89   4.307%   $104.1923   $104.19   $104.20   $104.20  
  Purchase #4 $22.30   9.827%   $24.4914   $24.49   $24.50   $24.50  
  Purchase #5 $86.54   5.548%   $91.3412   $91.34   $91.35   $91.30  
  Purchase #6 $73.90   3.362%   $76.3845   $76.38   $76.40   $76.40  
  Purchase #7 $216.80   7.873%   $233.8687   $233.87   $233.85   $233.90  
  7 purchase totals = $855.14       $919.5975   $919.58   $919.60   $919.60