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 $246.71   5.106%   $259.307   $259.31   $259.30   $259.30  
  Purchase #2 $60.61   8.389%   $65.6946   $65.69   $65.70   $65.70  
  Purchase #3 $231.37   4.400%   $241.5503   $241.55   $241.55   $241.60  
  Purchase #4 $216.26   10.378%   $238.7035   $238.70   $238.70   $238.70  
  Purchase #5 $33.85   8.823%   $36.8366   $36.84   $36.85   $36.80  
  Purchase #6 $5.39   8.675%   $5.8576   $5.86   $5.85   $5.90  
  Purchase #7 $5.30   3.560%   $5.4887   $5.49   $5.50   $5.50  
  7 purchase totals = $799.49       $853.4383   $853.44   $853.45   $853.50