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 $69.49   5.757%   $73.4905   $73.49   $73.50   $73.50  
  Purchase #2 $178.64   11.359%   $198.9317   $198.93   $198.95   $198.90  
  Purchase #3 $36.29   4.293%   $37.8479   $37.85   $37.85   $37.80  
  Purchase #4 $222.92   7.243%   $239.0661   $239.07   $239.05   $239.10  
  Purchase #5 $122.69   9.408%   $134.2327   $134.23   $134.25   $134.20  
  Purchase #6 $150.50   4.792%   $157.712   $157.71   $157.70   $157.70  
  Purchase #7 $111.81   4.184%   $116.4881   $116.49   $116.50   $116.50  
  7 purchase totals = $892.34       $957.7690   $957.77   $957.80   $957.70