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 $246.33   5.575%   $260.0629   $260.06   $260.05   $260.10  
  Purchase #2 $52.40   3.152%   $54.0516   $54.05   $54.05   $54.10  
  Purchase #3 $96.27   11.364%   $107.2101   $107.21   $107.20   $107.20  
  Purchase #4 $107.63   5.454%   $113.5001   $113.50   $113.50   $113.50  
  Purchase #5 $98.78   13.551%   $112.1657   $112.17   $112.15   $112.20  
  Purchase #6 $77.90   5.796%   $82.4151   $82.42   $82.40   $82.40  
  Purchase #7 $33.28   6.283%   $35.371   $35.37   $35.35   $35.40  
  7 purchase totals = $712.59       $764.7765   $764.78   $764.70   $764.90