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 $22.96   11.527%   $25.6066   $25.61   $25.60   $25.60  
  Purchase #2 $213.65   8.122%   $231.0027   $231.00   $231.00   $231.00  
  Purchase #3 $130.93   8.666%   $142.2764   $142.28   $142.30   $142.30  
  Purchase #4 $125.58   5.619%   $132.6363   $132.64   $132.65   $132.60  
  Purchase #5 $95.32   13.811%   $108.4846   $108.48   $108.50   $108.50  
  Purchase #6 $8.88   6.735%   $9.4781   $9.48   $9.50   $9.50  
  Purchase #7 $147.41   5.471%   $155.4748   $155.47   $155.45   $155.50  
  7 purchase totals = $744.73       $804.9595   $804.96   $805.00   $805.00