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 $23.27   6.201%   $24.713   $24.71   $24.70   $24.70  
  Purchase #2 $166.36   10.381%   $183.6298   $183.63   $183.65   $183.60  
  Purchase #3 $139.55   9.842%   $153.2845   $153.28   $153.30   $153.30  
  Purchase #4 $84.76   5.863%   $89.7295   $89.73   $89.75   $89.70  
  Purchase #5 $218.88   12.435%   $246.0977   $246.10   $246.10   $246.10  
  Purchase #6 $154.63   11.364%   $172.2022   $172.20   $172.20   $172.20  
  Purchase #7 $112.90   3.525%   $116.8797   $116.88   $116.90   $116.90  
  7 purchase totals = $900.35       $986.5364   $986.53   $986.60   $986.50