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 $176.31   8.440%   $191.1906   $191.19   $191.20   $191.20  
  Purchase #2 $217.27   10.296%   $239.6401   $239.64   $239.65   $239.60  
  Purchase #3 $83.76   8.766%   $91.1024   $91.10   $91.10   $91.10  
  Purchase #4 $16.77   9.512%   $18.3652   $18.37   $18.35   $18.40  
  Purchase #5 $232.99   8.341%   $252.4237   $252.42   $252.40   $252.40  
  Purchase #6 $27.33   12.588%   $30.7703   $30.77   $30.75   $30.80  
  Purchase #7 $114.98   9.321%   $125.6973   $125.70   $125.70   $125.70  
  7 purchase totals = $869.41       $949.1896   $949.19   $949.15   $949.20