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 $179.89   8.118%   $194.4935   $194.49   $194.50   $194.50  
  Purchase #2 $247.72   9.620%   $271.5507   $271.55   $271.55   $271.60  
  Purchase #3 $212.71   13.683%   $241.8151   $241.82   $241.80   $241.80  
  Purchase #4 $104.28   9.570%   $114.2596   $114.26   $114.25   $114.30  
  Purchase #5 $91.34   8.381%   $98.9952   $99.00   $99.00   $99.00  
  Purchase #6 $209.37   12.863%   $236.3013   $236.30   $236.30   $236.30  
  Purchase #7 $86.63   10.617%   $95.8275   $95.83   $95.85   $95.80  
  7 purchase totals = $1,131.94       $1,253.2429   $1,253.25   $1,253.25   $1,253.30