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 $249.94   9.772%   $274.3641   $274.36   $274.35   $274.40  
  Purchase #2 $209.91   7.842%   $226.3711   $226.37   $226.35   $226.40  
  Purchase #3 $50.46   13.628%   $57.3367   $57.34   $57.35   $57.30  
  Purchase #4 $201.36   4.496%   $210.4131   $210.41   $210.40   $210.40  
  Purchase #5 $109.44   5.768%   $115.7525   $115.75   $115.75   $115.80  
  Purchase #6 $52.61   9.318%   $57.5122   $57.51   $57.50   $57.50  
  Purchase #7 $236.82   7.147%   $253.7455   $253.75   $253.75   $253.70  
  7 purchase totals = $1,110.54       $1,195.4952   $1,195.49   $1,195.45   $1,195.50