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 $58.71   8.721%   $63.8301   $63.83   $63.85   $63.80  
  Purchase #2 $54.62   3.626%   $56.6005   $56.60   $56.60   $56.60  
  Purchase #3 $216.60   11.149%   $240.7487   $240.75   $240.75   $240.70  
  Purchase #4 $84.78   8.522%   $92.005   $92.01   $92.00   $92.00  
  Purchase #5 $11.81   10.195%   $13.014   $13.01   $13.00   $13.00  
  Purchase #6 $126.92   4.482%   $132.6086   $132.61   $132.60   $132.60  
  Purchase #7 $81.37   8.614%   $88.3792   $88.38   $88.40   $88.40  
  7 purchase totals = $634.81       $687.1861   $687.19   $687.20   $687.10