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 $151.57   3.551%   $156.9523   $156.95   $156.95   $157.00  
  Purchase #2 $189.35   11.245%   $210.6424   $210.64   $210.65   $210.60  
  Purchase #3 $207.32   3.844%   $215.2894   $215.29   $215.30   $215.30  
  Purchase #4 $126.83   7.784%   $136.7024   $136.70   $136.70   $136.70  
  Purchase #5 $216.79   4.807%   $227.2111   $227.21   $227.20   $227.20  
  Purchase #6 $53.67   4.434%   $56.0497   $56.05   $56.05   $56.00  
  Purchase #7 $57.64   10.393%   $63.6305   $63.63   $63.65   $63.60  
  7 purchase totals = $1,003.17       $1,066.4778   $1,066.47   $1,066.50   $1,066.40