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 $68.81   7.747%   $74.1407   $74.14   $74.15   $74.10  
  Purchase #2 $60.25   5.114%   $63.3312   $63.33   $63.35   $63.30  
  Purchase #3 $119.57   5.715%   $126.4034   $126.40   $126.40   $126.40  
  Purchase #4 $69.81   4.805%   $73.1644   $73.16   $73.15   $73.20  
  Purchase #5 $231.92   6.397%   $246.7559   $246.76   $246.75   $246.80  
  Purchase #6 $21.26   4.260%   $22.1657   $22.17   $22.15   $22.20  
  Purchase #7 $140.34   12.711%   $158.1786   $158.18   $158.20   $158.20  
  7 purchase totals = $711.96       $764.1399   $764.14   $764.15   $764.20