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 $211.64   4.111%   $220.3405   $220.34   $220.35   $220.30  
  Purchase #2 $210.41   12.694%   $237.1194   $237.12   $237.10   $237.10  
  Purchase #3 $154.99   6.206%   $164.6087   $164.61   $164.60   $164.60  
  Purchase #4 $56.83   9.168%   $62.0402   $62.04   $62.05   $62.00  
  Purchase #5 $187.97   13.250%   $212.876   $212.88   $212.90   $212.90  
  Purchase #6 $208.63   6.509%   $222.2097   $222.21   $222.20   $222.20  
  Purchase #7 $30.56   13.122%   $34.5701   $34.57   $34.55   $34.60  
  7 purchase totals = $1,061.03       $1,153.7646   $1,153.77   $1,153.75   $1,153.70