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 $207.28   13.532%   $235.3291   $235.33   $235.35   $235.30  
  Purchase #2 $226.33   13.522%   $256.9343   $256.93   $256.95   $256.90  
  Purchase #3 $248.99   10.379%   $274.8327   $274.83   $274.85   $274.80  
  Purchase #4 $22.86   4.302%   $23.8434   $23.84   $23.85   $23.80  
  Purchase #5 $149.80   3.255%   $154.676   $154.68   $154.70   $154.70  
  Purchase #6 $98.51   4.447%   $102.8907   $102.89   $102.90   $102.90  
  Purchase #7 $190.53   3.125%   $196.4841   $196.48   $196.50   $196.50  
  7 purchase totals = $1,144.30       $1,244.9903   $1,244.98   $1,245.10   $1,244.90