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 $96.53   8.799%   $105.0237   $105.02   $105.00   $105.00  
  Purchase #2 $51.42   13.860%   $58.5468   $58.55   $58.55   $58.50  
  Purchase #3 $56.42   5.358%   $59.443   $59.44   $59.45   $59.40  
  Purchase #4 $26.69   6.419%   $28.4032   $28.40   $28.40   $28.40  
  Purchase #5 $182.49   11.838%   $204.0932   $204.09   $204.10   $204.10  
  Purchase #6 $161.73   12.537%   $182.0061   $182.01   $182.00   $182.00  
  Purchase #7 $159.86   3.315%   $165.1594   $165.16   $165.15   $165.20  
  7 purchase totals = $735.14       $802.6754   $802.67   $802.65   $802.60