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 $24.31   7.860%   $26.2208   $26.22   $26.20   $26.20  
  Purchase #2 $105.88   10.359%   $116.8481   $116.85   $116.85   $116.80  
  Purchase #3 $22.62   7.606%   $24.3405   $24.34   $24.35   $24.30  
  Purchase #4 $60.46   11.239%   $67.2551   $67.26   $67.25   $67.30  
  Purchase #5 $175.91   5.338%   $185.3001   $185.30   $185.30   $185.30  
  Purchase #6 $195.62   13.363%   $221.7607   $221.76   $221.75   $221.80  
  Purchase #7 $111.56   4.817%   $116.9338   $116.93   $116.95   $116.90  
  7 purchase totals = $696.36       $758.6591   $758.66   $758.65   $758.60