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 $65.71   11.180%   $73.0564   $73.06   $73.05   $73.10  
  Purchase #2 $242.25   10.117%   $266.7584   $266.76   $266.75   $266.80  
  Purchase #3 $8.56   10.319%   $9.4433   $9.44   $9.45   $9.40  
  Purchase #4 $6.39   4.291%   $6.6642   $6.66   $6.65   $6.70  
  Purchase #5 $47.86   3.437%   $49.5049   $49.50   $49.50   $49.50  
  Purchase #6 $165.83   6.345%   $176.3519   $176.35   $176.35   $176.40  
  Purchase #7 $227.53   11.847%   $254.4855   $254.49   $254.50   $254.50  
  7 purchase totals = $764.13       $836.2646   $836.26   $836.25   $836.40