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 $65.63   11.751%   $73.3422   $73.34   $73.35   $73.30  
  Purchase #2 $183.81   8.451%   $199.3438   $199.34   $199.35   $199.30  
  Purchase #3 $100.49   4.520%   $105.0321   $105.03   $105.05   $105.00  
  Purchase #4 $85.66   12.289%   $96.1868   $96.19   $96.20   $96.20  
  Purchase #5 $161.70   12.244%   $181.4985   $181.50   $181.50   $181.50  
  Purchase #6 $193.44   6.719%   $206.4372   $206.44   $206.45   $206.40  
  Purchase #7 $116.68   8.213%   $126.2629   $126.26   $126.25   $126.30  
  7 purchase totals = $907.41       $988.1035   $988.10   $988.15   $988.00