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 $48.28   12.742%   $54.4318   $54.43   $54.45   $54.40  
  Purchase #2 $237.43   3.455%   $245.6332   $245.63   $245.65   $245.60  
  Purchase #3 $27.61   6.362%   $29.3665   $29.37   $29.35   $29.40  
  Purchase #4 $209.82   3.166%   $216.4629   $216.46   $216.45   $216.50  
  Purchase #5 $205.70   12.725%   $231.8753   $231.88   $231.90   $231.90  
  Purchase #6 $110.37   3.584%   $114.3257   $114.33   $114.35   $114.30  
  Purchase #7 $236.94   12.471%   $266.4888   $266.49   $266.50   $266.50  
  7 purchase totals = $1,076.15       $1,158.5842   $1,158.59   $1,158.65   $1,158.60