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 $61.68   5.842%   $65.2833   $65.28   $65.30   $65.30  
  Purchase #2 $44.70   7.384%   $48.0006   $48.00   $48.00   $48.00  
  Purchase #3 $235.48   11.143%   $261.7195   $261.72   $261.70   $261.70  
  Purchase #4 $119.86   9.463%   $131.2024   $131.20   $131.20   $131.20  
  Purchase #5 $180.27   4.614%   $188.5877   $188.59   $188.60   $188.60  
  Purchase #6 $60.75   5.740%   $64.2371   $64.24   $64.25   $64.20  
  Purchase #7 $63.32   10.539%   $69.9933   $69.99   $70.00   $70.00  
  7 purchase totals = $766.06       $829.0239   $829.02   $829.05   $829.00