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 $208.31   10.669%   $230.5346   $230.53   $230.55   $230.50  
  Purchase #2 $71.27   11.106%   $79.1852   $79.19   $79.20   $79.20  
  Purchase #3 $155.45   11.533%   $173.378   $173.38   $173.40   $173.40  
  Purchase #4 $41.64   7.233%   $44.6518   $44.65   $44.65   $44.70  
  Purchase #5 $83.86   13.821%   $95.4503   $95.45   $95.45   $95.50  
  Purchase #6 $115.99   3.836%   $120.4394   $120.44   $120.45   $120.40  
  Purchase #7 $45.62   12.825%   $51.4708   $51.47   $51.45   $51.50  
  7 purchase totals = $722.14       $795.1101   $795.11   $795.15   $795.20