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 $239.72   11.630%   $267.5994   $267.60   $267.60   $267.60  
  Purchase #2 $232.54   8.229%   $251.6757   $251.68   $251.70   $251.70  
  Purchase #3 $83.72   13.265%   $94.8255   $94.83   $94.85   $94.80  
  Purchase #4 $89.65   12.599%   $100.945   $100.95   $100.95   $100.90  
  Purchase #5 $158.25   6.552%   $168.6185   $168.62   $168.60   $168.60  
  Purchase #6 $8.85   11.864%   $9.9   $9.90   $9.90   $9.90  
  Purchase #7 $46.66   9.838%   $51.2504   $51.25   $51.25   $51.30  
  7 purchase totals = $859.39       $944.8145   $944.83   $944.85   $944.80