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 $208.83   3.416%   $215.9636   $215.96   $215.95   $216.00  
  Purchase #2 $32.42   12.188%   $36.3713   $36.37   $36.35   $36.40  
  Purchase #3 $49.82   11.594%   $55.5961   $55.60   $55.60   $55.60  
  Purchase #4 $32.25   7.707%   $34.7355   $34.74   $34.75   $34.70  
  Purchase #5 $36.91   4.738%   $38.6588   $38.66   $38.65   $38.70  
  Purchase #6 $116.87   13.124%   $132.208   $132.21   $132.20   $132.20  
  Purchase #7 $211.71   12.801%   $238.811   $238.81   $238.80   $238.80  
  7 purchase totals = $688.81       $752.3443   $752.35   $752.30   $752.40