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 $207.48   7.482%   $223.0037   $223.00   $223.00   $223.00  
  Purchase #2 $6.63   13.714%   $7.5392   $7.54   $7.55   $7.50  
  Purchase #3 $238.55   6.406%   $253.8315   $253.83   $253.85   $253.80  
  Purchase #4 $55.27   12.141%   $61.9803   $61.98   $62.00   $62.00  
  Purchase #5 $49.62   7.782%   $53.4814   $53.48   $53.50   $53.50  
  Purchase #6 $59.99   5.452%   $63.2607   $63.26   $63.25   $63.30  
  Purchase #7 $238.73   11.233%   $265.5465   $265.55   $265.55   $265.50  
  7 purchase totals = $856.27       $928.6433   $928.64   $928.70   $928.60