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 $88.36   8.688%   $96.0367   $96.04   $96.05   $96.00  
  Purchase #2 $24.38   10.198%   $26.8663   $26.87   $26.85   $26.90  
  Purchase #3 $228.85   6.775%   $244.3546   $244.35   $244.35   $244.40  
  Purchase #4 $89.82   6.139%   $95.334   $95.33   $95.35   $95.30  
  Purchase #5 $186.69   7.280%   $200.281   $200.28   $200.30   $200.30  
  Purchase #6 $5.53   9.533%   $6.0572   $6.06   $6.05   $6.10  
  Purchase #7 $8.30   3.569%   $8.5962   $8.60   $8.60   $8.60  
  7 purchase totals = $631.93       $677.5260   $677.53   $677.55   $677.60