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 $33.54   9.827%   $36.836   $36.84   $36.85   $36.80  
  Purchase #2 $109.34   9.457%   $119.6803   $119.68   $119.70   $119.70  
  Purchase #3 $63.79   4.426%   $66.6133   $66.61   $66.60   $66.60  
  Purchase #4 $23.79   5.167%   $25.0192   $25.02   $25.00   $25.00  
  Purchase #5 $144.35   12.165%   $161.9102   $161.91   $161.90   $161.90  
  Purchase #6 $233.56   9.232%   $255.1223   $255.12   $255.10   $255.10  
  Purchase #7 $117.25   7.707%   $126.2865   $126.29   $126.30   $126.30  
  7 purchase totals = $725.62       $791.4678   $791.47   $791.45   $791.40