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 $113.87   9.318%   $124.4804   $124.48   $124.50   $124.50  
  Purchase #2 $84.66   4.273%   $88.2775   $88.28   $88.30   $88.30  
  Purchase #3 $45.25   5.163%   $47.5863   $47.59   $47.60   $47.60  
  Purchase #4 $46.76   11.713%   $52.237   $52.24   $52.25   $52.20  
  Purchase #5 $247.61   6.404%   $263.4669   $263.47   $263.45   $263.50  
  Purchase #6 $13.50   10.255%   $14.8844   $14.88   $14.90   $14.90  
  Purchase #7 $233.27   3.398%   $241.1965   $241.20   $241.20   $241.20  
  7 purchase totals = $784.92       $832.1290   $832.14   $832.20   $832.20