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 $93.99   4.607%   $98.3201   $98.32   $98.30   $98.30  
  Purchase #2 $202.69   12.336%   $227.6938   $227.69   $227.70   $227.70  
  Purchase #3 $66.80   13.354%   $75.7205   $75.72   $75.70   $75.70  
  Purchase #4 $92.63   4.539%   $96.8345   $96.83   $96.85   $96.80  
  Purchase #5 $98.86   7.509%   $106.2834   $106.28   $106.30   $106.30  
  Purchase #6 $71.56   8.542%   $77.6727   $77.67   $77.65   $77.70  
  Purchase #7 $183.71   4.197%   $191.4203   $191.42   $191.40   $191.40  
  7 purchase totals = $810.24       $873.9453   $873.93   $873.90   $873.90