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 $61.88   8.536%   $67.1621   $67.16   $67.15   $67.20  
  Purchase #2 $168.92   9.494%   $184.9573   $184.96   $184.95   $185.00  
  Purchase #3 $213.98   3.680%   $221.8545   $221.85   $221.85   $221.90  
  Purchase #4 $169.79   3.766%   $176.1843   $176.18   $176.20   $176.20  
  Purchase #5 $49.33   3.371%   $50.9929   $50.99   $51.00   $51.00  
  Purchase #6 $211.28   10.299%   $233.0397   $233.04   $233.05   $233.00  
  Purchase #7 $58.83   9.824%   $64.6095   $64.61   $64.60   $64.60  
  7 purchase totals = $934.01       $998.8003   $998.79   $998.80   $998.90