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 $132.99   12.608%   $149.7574   $149.76   $149.75   $149.80  
  Purchase #2 $30.94   11.384%   $34.4622   $34.46   $34.45   $34.50  
  Purchase #3 $167.90   7.522%   $180.5294   $180.53   $180.55   $180.50  
  Purchase #4 $59.27   5.772%   $62.6911   $62.69   $62.70   $62.70  
  Purchase #5 $5.27   13.750%   $5.9946   $5.99   $6.00   $6.00  
  Purchase #6 $66.76   11.756%   $74.6083   $74.61   $74.60   $74.60  
  Purchase #7 $104.53   11.164%   $116.1997   $116.20   $116.20   $116.20  
  7 purchase totals = $567.66       $624.2427   $624.24   $624.25   $624.30