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 $56.96   5.628%   $60.1657   $60.17   $60.15   $60.20  
  Purchase #2 $14.27   9.118%   $15.5711   $15.57   $15.55   $15.60  
  Purchase #3 $118.26   7.615%   $127.2655   $127.27   $127.25   $127.30  
  Purchase #4 $62.42   6.653%   $66.5728   $66.57   $66.55   $66.60  
  Purchase #5 $7.78   10.388%   $8.5882   $8.59   $8.60   $8.60  
  Purchase #6 $218.44   8.243%   $236.446   $236.45   $236.45   $236.40  
  Purchase #7 $241.55   12.706%   $272.2413   $272.24   $272.25   $272.20  
  7 purchase totals = $719.68       $786.8506   $786.86   $786.80   $786.90