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 $25.76   8.748%   $28.0135   $28.01   $28.00   $28.00  
  Purchase #2 $112.48   13.482%   $127.6446   $127.64   $127.65   $127.60  
  Purchase #3 $40.74   7.435%   $43.769   $43.77   $43.75   $43.80  
  Purchase #4 $84.82   13.149%   $95.973   $95.97   $95.95   $96.00  
  Purchase #5 $227.88   13.325%   $258.245   $258.25   $258.25   $258.20  
  Purchase #6 $59.47   8.451%   $64.4958   $64.50   $64.50   $64.50  
  Purchase #7 $64.89   5.399%   $68.3934   $68.39   $68.40   $68.40  
  7 purchase totals = $616.04       $686.5343   $686.53   $686.50   $686.50