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 $53.96   10.354%   $59.547   $59.55   $59.55   $59.50  
  Purchase #2 $43.92   7.522%   $47.2237   $47.22   $47.20   $47.20  
  Purchase #3 $95.74   12.285%   $107.5017   $107.50   $107.50   $107.50  
  Purchase #4 $38.79   5.731%   $41.0131   $41.01   $41.00   $41.00  
  Purchase #5 $76.71   7.262%   $82.2807   $82.28   $82.30   $82.30  
  Purchase #6 $178.80   11.684%   $199.691   $199.69   $199.70   $199.70  
  Purchase #7 $131.84   13.757%   $149.9772   $149.98   $150.00   $150.00  
  7 purchase totals = $619.76       $687.2344   $687.23   $687.25   $687.20