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 $228.27   4.410%   $238.3367   $238.34   $238.35   $238.30  
  Purchase #2 $222.69   8.319%   $241.2156   $241.22   $241.20   $241.20  
  Purchase #3 $143.75   8.429%   $155.8667   $155.87   $155.85   $155.90  
  Purchase #4 $60.61   8.207%   $65.5843   $65.58   $65.60   $65.60  
  Purchase #5 $92.32   3.492%   $95.5438   $95.54   $95.55   $95.50  
  Purchase #6 $196.74   10.403%   $217.2069   $217.21   $217.20   $217.20  
  Purchase #7 $183.53   3.151%   $189.313   $189.31   $189.30   $189.30  
  7 purchase totals = $1,127.91       $1,203.0670   $1,203.07   $1,203.05   $1,203.00