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 $32.94   4.691%   $34.4852   $34.49   $34.50   $34.50  
  Purchase #2 $87.47   5.382%   $92.1776   $92.18   $92.20   $92.20  
  Purchase #3 $227.55   12.391%   $255.7457   $255.75   $255.75   $255.70  
  Purchase #4 $59.74   3.220%   $61.6636   $61.66   $61.65   $61.70  
  Purchase #5 $13.46   9.191%   $14.6971   $14.70   $14.70   $14.70  
  Purchase #6 $227.34   6.735%   $242.6513   $242.65   $242.65   $242.70  
  Purchase #7 $55.61   5.569%   $58.7069   $58.71   $58.70   $58.70  
  7 purchase totals = $704.11       $760.1274   $760.14   $760.15   $760.20