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 $98.83   13.570%   $112.2412   $112.24   $112.25   $112.20  
  Purchase #2 $55.99   12.392%   $62.9283   $62.93   $62.95   $62.90  
  Purchase #3 $67.53   11.135%   $75.0495   $75.05   $75.05   $75.00  
  Purchase #4 $64.29   4.784%   $67.3656   $67.37   $67.35   $67.40  
  Purchase #5 $184.62   13.729%   $209.9665   $209.97   $209.95   $210.00  
  Purchase #6 $47.85   3.224%   $49.3927   $49.39   $49.40   $49.40  
  Purchase #7 $149.85   9.637%   $164.291   $164.29   $164.30   $164.30  
  7 purchase totals = $668.96       $741.2348   $741.24   $741.25   $741.20