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 $230.38   6.260%   $244.8018   $244.80   $244.80   $244.80  
  Purchase #2 $228.46   3.275%   $235.9421   $235.94   $235.95   $235.90  
  Purchase #3 $237.85   6.510%   $253.334   $253.33   $253.35   $253.30  
  Purchase #4 $5.63   12.418%   $6.3291   $6.33   $6.35   $6.30  
  Purchase #5 $223.90   7.507%   $240.7082   $240.71   $240.70   $240.70  
  Purchase #6 $52.64   6.854%   $56.2479   $56.25   $56.25   $56.20  
  Purchase #7 $194.77   10.848%   $215.8986   $215.90   $215.90   $215.90  
  7 purchase totals = $1,173.63       $1,253.2617   $1,253.26   $1,253.30   $1,253.10