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 $196.49   4.304%   $204.9469   $204.95   $204.95   $204.90  
  Purchase #2 $48.49   8.193%   $52.4628   $52.46   $52.45   $52.50  
  Purchase #3 $150.81   5.558%   $159.192   $159.19   $159.20   $159.20  
  Purchase #4 $206.25   12.287%   $231.5919   $231.59   $231.60   $231.60  
  Purchase #5 $87.63   3.537%   $90.7295   $90.73   $90.75   $90.70  
  Purchase #6 $23.27   13.407%   $26.3898   $26.39   $26.40   $26.40  
  Purchase #7 $244.66   5.813%   $258.8821   $258.88   $258.90   $258.90  
  7 purchase totals = $957.60       $1,024.1950   $1,024.19   $1,024.25   $1,024.20