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 $35.99   8.709%   $39.1244   $39.12   $39.10   $39.10  
  Purchase #2 $66.42   10.667%   $73.505   $73.51   $73.50   $73.50  
  Purchase #3 $45.36   4.359%   $47.3372   $47.34   $47.35   $47.30  
  Purchase #4 $247.89   7.419%   $266.281   $266.28   $266.30   $266.30  
  Purchase #5 $61.80   8.657%   $67.15   $67.15   $67.15   $67.20  
  Purchase #6 $214.85   5.440%   $226.5378   $226.54   $226.55   $226.50  
  Purchase #7 $37.92   5.629%   $40.0545   $40.05   $40.05   $40.10  
  7 purchase totals = $710.23       $759.9899   $759.99   $760.00   $760.00