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 $250.83   4.866%   $263.0354   $263.04   $263.05   $263.00  
  Purchase #2 $31.63   7.178%   $33.9004   $33.90   $33.90   $33.90  
  Purchase #3 $13.51   4.174%   $14.0739   $14.07   $14.05   $14.10  
  Purchase #4 $93.87   13.127%   $106.1923   $106.19   $106.20   $106.20  
  Purchase #5 $120.66   9.444%   $132.0551   $132.06   $132.05   $132.10  
  Purchase #6 $66.57   3.794%   $69.0957   $69.10   $69.10   $69.10  
  Purchase #7 $120.82   4.514%   $126.2738   $126.27   $126.25   $126.30  
  7 purchase totals = $697.89       $744.6266   $744.63   $744.60   $744.70