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 $57.44   7.804%   $61.9226   $61.92   $61.90   $61.90  
  Purchase #2 $204.50   9.848%   $224.6392   $224.64   $224.65   $224.60  
  Purchase #3 $137.64   13.463%   $156.1705   $156.17   $156.15   $156.20  
  Purchase #4 $53.41   9.480%   $58.4733   $58.47   $58.45   $58.50  
  Purchase #5 $159.71   10.633%   $176.692   $176.69   $176.70   $176.70  
  Purchase #6 $121.76   8.400%   $131.9878   $131.99   $132.00   $132.00  
  Purchase #7 $191.42   12.170%   $214.7158   $214.72   $214.70   $214.70  
  7 purchase totals = $925.88       $1,024.6012   $1,024.60   $1,024.55   $1,024.60