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 $190.86   8.763%   $207.5851   $207.59   $207.60   $207.60  
  Purchase #2 $72.81   12.182%   $81.6797   $81.68   $81.70   $81.70  
  Purchase #3 $19.77   5.673%   $20.8916   $20.89   $20.90   $20.90  
  Purchase #4 $242.84   5.615%   $256.4755   $256.48   $256.50   $256.50  
  Purchase #5 $68.25   7.447%   $73.3326   $73.33   $73.35   $73.30  
  Purchase #6 $249.57   4.345%   $260.4138   $260.41   $260.40   $260.40  
  Purchase #7 $10.72   13.211%   $12.1362   $12.14   $12.15   $12.10  
  7 purchase totals = $854.82       $912.5145   $912.52   $912.60   $912.50