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 $77.85   6.171%   $82.6541   $82.65   $82.65   $82.70  
  Purchase #2 $201.69   5.776%   $213.3396   $213.34   $213.35   $213.30  
  Purchase #3 $16.95   8.655%   $18.417   $18.42   $18.40   $18.40  
  Purchase #4 $226.62   4.499%   $236.8156   $236.82   $236.80   $236.80  
  Purchase #5 $183.55   3.209%   $189.4401   $189.44   $189.45   $189.40  
  Purchase #6 $16.71   3.283%   $17.2586   $17.26   $17.25   $17.30  
  Purchase #7 $62.73   9.277%   $68.5495   $68.55   $68.55   $68.50  
  7 purchase totals = $786.10       $826.4745   $826.48   $826.45   $826.40