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 $242.94   8.145%   $262.7275   $262.73   $262.75   $262.70  
  Purchase #2 $6.92   8.189%   $7.4867   $7.49   $7.50   $7.50  
  Purchase #3 $238.69   7.200%   $255.8757   $255.88   $255.90   $255.90  
  Purchase #4 $80.46   5.378%   $84.7871   $84.79   $84.80   $84.80  
  Purchase #5 $20.54   11.594%   $22.9214   $22.92   $22.90   $22.90  
  Purchase #6 $96.56   8.239%   $104.5156   $104.52   $104.50   $104.50  
  Purchase #7 $14.37   6.471%   $15.2999   $15.30   $15.30   $15.30  
  7 purchase totals = $700.48       $753.6139   $753.63   $753.65   $753.60