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 $56.29   13.736%   $64.022   $64.02   $64.00   $64.00  
  Purchase #2 $248.40   8.124%   $268.58   $268.58   $268.60   $268.60  
  Purchase #3 $115.78   11.493%   $129.0866   $129.09   $129.10   $129.10  
  Purchase #4 $64.84   11.504%   $72.2992   $72.30   $72.30   $72.30  
  Purchase #5 $101.89   9.828%   $111.9037   $111.90   $111.90   $111.90  
  Purchase #6 $12.74   3.621%   $13.2013   $13.20   $13.20   $13.20  
  Purchase #7 $91.95   4.413%   $96.0078   $96.01   $96.00   $96.00  
  7 purchase totals = $691.89       $755.1006   $755.10   $755.10   $755.10