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 $213.36   5.150%   $224.348   $224.35   $224.35   $224.30  
  Purchase #2 $70.41   4.845%   $73.8214   $73.82   $73.80   $73.80  
  Purchase #3 $56.67   13.742%   $64.4576   $64.46   $64.45   $64.50  
  Purchase #4 $203.99   6.827%   $217.9164   $217.92   $217.90   $217.90  
  Purchase #5 $114.91   7.831%   $123.9086   $123.91   $123.90   $123.90  
  Purchase #6 $49.71   13.874%   $56.6068   $56.61   $56.60   $56.60  
  Purchase #7 $91.77   5.326%   $96.6577   $96.66   $96.65   $96.70  
  7 purchase totals = $800.82       $857.7165   $857.73   $857.65   $857.70