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 $24.63   6.463%   $26.2218   $26.22   $26.20   $26.20  
  Purchase #2 $70.56   5.535%   $74.4655   $74.47   $74.45   $74.50  
  Purchase #3 $101.55   8.178%   $109.8548   $109.85   $109.85   $109.90  
  Purchase #4 $55.71   4.637%   $58.2933   $58.29   $58.30   $58.30  
  Purchase #5 $199.93   4.360%   $208.6469   $208.65   $208.65   $208.60  
  Purchase #6 $235.98   9.773%   $259.0423   $259.04   $259.05   $259.00  
  Purchase #7 $17.74   11.719%   $19.819   $19.82   $19.80   $19.80  
  7 purchase totals = $706.10       $756.3436   $756.34   $756.30   $756.30