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 $68.97   6.831%   $73.6813   $73.68   $73.70   $73.70  
  Purchase #2 $207.45   4.205%   $216.1733   $216.17   $216.15   $216.20  
  Purchase #3 $27.96   9.187%   $30.5287   $30.53   $30.55   $30.50  
  Purchase #4 $247.80   9.735%   $271.9233   $271.92   $271.90   $271.90  
  Purchase #5 $45.60   11.601%   $50.8901   $50.89   $50.90   $50.90  
  Purchase #6 $226.48   10.226%   $249.6398   $249.64   $249.65   $249.60  
  Purchase #7 $96.83   10.152%   $106.6602   $106.66   $106.65   $106.70  
  7 purchase totals = $921.09       $999.4967   $999.49   $999.50   $999.50