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 $226.99   11.741%   $253.6409   $253.64   $253.65   $253.60  
  Purchase #2 $150.25   12.495%   $169.0237   $169.02   $169.00   $169.00  
  Purchase #3 $68.80   10.603%   $76.0949   $76.09   $76.10   $76.10  
  Purchase #4 $243.38   6.784%   $259.8909   $259.89   $259.90   $259.90  
  Purchase #5 $175.57   11.501%   $195.7623   $195.76   $195.75   $195.80  
  Purchase #6 $219.27   6.698%   $233.9567   $233.96   $233.95   $234.00  
  Purchase #7 $172.49   8.474%   $187.1068   $187.11   $187.10   $187.10  
  7 purchase totals = $1,256.75       $1,375.4762   $1,375.47   $1,375.45   $1,375.50