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 $95.48   7.776%   $102.9045   $102.90   $102.90   $102.90  
  Purchase #2 $53.67   5.104%   $56.4093   $56.41   $56.40   $56.40  
  Purchase #3 $186.90   11.617%   $208.6122   $208.61   $208.60   $208.60  
  Purchase #4 $171.35   6.726%   $182.875   $182.88   $182.90   $182.90  
  Purchase #5 $25.64   13.103%   $28.9996   $29.00   $29.00   $29.00  
  Purchase #6 $58.33   12.236%   $65.4673   $65.47   $65.45   $65.50  
  Purchase #7 $67.76   7.745%   $73.008   $73.01   $73.00   $73.00  
  7 purchase totals = $659.13       $718.2759   $718.28   $718.25   $718.30