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 $41.47   5.228%   $43.6381   $43.64   $43.65   $43.60  
  Purchase #2 $92.36   11.455%   $102.9398   $102.94   $102.95   $102.90  
  Purchase #3 $199.84   7.744%   $215.3156   $215.32   $215.30   $215.30  
  Purchase #4 $207.96   12.471%   $233.8947   $233.89   $233.90   $233.90  
  Purchase #5 $6.40   11.509%   $7.1366   $7.14   $7.15   $7.10  
  Purchase #6 $123.96   8.749%   $134.8053   $134.81   $134.80   $134.80  
  Purchase #7 $208.40   5.464%   $219.787   $219.79   $219.80   $219.80  
  7 purchase totals = $880.39       $957.5171   $957.53   $957.55   $957.40