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 $86.55   13.255%   $98.0222   $98.02   $98.00   $98.00  
  Purchase #2 $52.66   9.779%   $57.8096   $57.81   $57.80   $57.80  
  Purchase #3 $31.36   5.198%   $32.9901   $32.99   $33.00   $33.00  
  Purchase #4 $37.36   13.849%   $42.534   $42.53   $42.55   $42.50  
  Purchase #5 $184.79   10.574%   $204.3297   $204.33   $204.35   $204.30  
  Purchase #6 $151.44   6.509%   $161.2972   $161.30   $161.30   $161.30  
  Purchase #7 $82.62   3.235%   $85.2928   $85.29   $85.30   $85.30  
  7 purchase totals = $626.78       $682.2756   $682.27   $682.30   $682.20