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 $190.48   8.263%   $206.2194   $206.22   $206.20   $206.20  
  Purchase #2 $24.35   12.345%   $27.356   $27.36   $27.35   $27.40  
  Purchase #3 $79.91   4.675%   $83.6458   $83.65   $83.65   $83.60  
  Purchase #4 $140.83   5.827%   $149.0362   $149.04   $149.05   $149.00  
  Purchase #5 $200.81   6.794%   $214.453   $214.45   $214.45   $214.50  
  Purchase #6 $31.99   7.105%   $34.2629   $34.26   $34.25   $34.30  
  Purchase #7 $212.98   10.490%   $235.3216   $235.32   $235.30   $235.30  
  7 purchase totals = $881.35       $950.2949   $950.30   $950.25   $950.30