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 $244.81   9.403%   $267.8295   $267.83   $267.85   $267.80  
  Purchase #2 $184.48   8.161%   $199.5354   $199.54   $199.55   $199.50  
  Purchase #3 $95.51   3.381%   $98.7392   $98.74   $98.75   $98.70  
  Purchase #4 $211.80   6.773%   $226.1452   $226.15   $226.15   $226.10  
  Purchase #5 $88.42   11.526%   $98.6113   $98.61   $98.60   $98.60  
  Purchase #6 $159.93   3.728%   $165.8922   $165.89   $165.90   $165.90  
  Purchase #7 $171.74   3.428%   $177.6272   $177.63   $177.65   $177.60  
  7 purchase totals = $1,156.69       $1,234.3800   $1,234.39   $1,234.45   $1,234.20