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 $41.34   5.615%   $43.6612   $43.66   $43.65   $43.70  
  Purchase #2 $190.41   7.326%   $204.3594   $204.36   $204.35   $204.40  
  Purchase #3 $249.26   4.541%   $260.5789   $260.58   $260.60   $260.60  
  Purchase #4 $148.92   10.728%   $164.8961   $164.90   $164.90   $164.90  
  Purchase #5 $78.30   9.685%   $85.8834   $85.88   $85.90   $85.90  
  Purchase #6 $22.27   3.407%   $23.0287   $23.03   $23.05   $23.00  
  Purchase #7 $201.97   6.329%   $214.7527   $214.75   $214.75   $214.80  
  7 purchase totals = $932.47       $997.1604   $997.16   $997.20   $997.30