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 $186.49   11.822%   $208.5368   $208.54   $208.55   $208.50  
  Purchase #2 $101.98   10.672%   $112.8633   $112.86   $112.85   $112.90  
  Purchase #3 $72.79   4.711%   $76.2191   $76.22   $76.20   $76.20  
  Purchase #4 $182.92   3.805%   $189.8801   $189.88   $189.90   $189.90  
  Purchase #5 $32.35   11.123%   $35.9483   $35.95   $35.95   $35.90  
  Purchase #6 $126.86   9.126%   $138.4372   $138.44   $138.45   $138.40  
  Purchase #7 $21.66   11.371%   $24.123   $24.12   $24.10   $24.10  
  7 purchase totals = $725.05       $786.0078   $786.01   $786.00   $785.90