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 $199.94   6.141%   $212.2183   $212.22   $212.20   $212.20  
  Purchase #2 $91.51   4.102%   $95.2637   $95.26   $95.25   $95.30  
  Purchase #3 $193.97   7.591%   $208.6943   $208.69   $208.70   $208.70  
  Purchase #4 $129.99   9.607%   $142.4781   $142.48   $142.50   $142.50  
  Purchase #5 $92.66   13.522%   $105.1895   $105.19   $105.20   $105.20  
  Purchase #6 $137.39   10.250%   $151.4725   $151.47   $151.45   $151.50  
  Purchase #7 $98.51   7.787%   $106.181   $106.18   $106.20   $106.20  
  7 purchase totals = $943.97       $1,021.4974   $1,021.49   $1,021.50   $1,021.60