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 $218.70   9.710%   $239.9358   $239.94   $239.95   $239.90  
  Purchase #2 $9.43   4.320%   $9.8374   $9.84   $9.85   $9.80  
  Purchase #3 $59.37   11.450%   $66.1679   $66.17   $66.15   $66.20  
  Purchase #4 $245.42   5.595%   $259.1512   $259.15   $259.15   $259.20  
  Purchase #5 $47.70   6.759%   $50.924   $50.92   $50.90   $50.90  
  Purchase #6 $63.37   7.168%   $67.9124   $67.91   $67.90   $67.90  
  Purchase #7 $21.87   9.743%   $24.0008   $24.00   $24.00   $24.00  
  7 purchase totals = $665.86       $717.9295   $717.93   $717.90   $717.90