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 $241.98   5.493%   $255.272   $255.27   $255.25   $255.30  
  Purchase #2 $174.49   3.140%   $179.969   $179.97   $179.95   $180.00  
  Purchase #3 $243.44   10.357%   $268.6531   $268.65   $268.65   $268.70  
  Purchase #4 $142.37   6.626%   $151.8034   $151.80   $151.80   $151.80  
  Purchase #5 $192.87   11.810%   $215.6479   $215.65   $215.65   $215.60  
  Purchase #6 $237.78   9.866%   $261.2394   $261.24   $261.25   $261.20  
  Purchase #7 $195.29   4.521%   $204.1191   $204.12   $204.10   $204.10  
  7 purchase totals = $1,428.22       $1,536.7039   $1,536.70   $1,536.65   $1,536.70