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 $178.86   8.210%   $193.5444   $193.54   $193.55   $193.50  
  Purchase #2 $186.42   10.446%   $205.8934   $205.89   $205.90   $205.90  
  Purchase #3 $186.67   11.642%   $208.4021   $208.40   $208.40   $208.40  
  Purchase #4 $35.65   5.553%   $37.6296   $37.63   $37.65   $37.60  
  Purchase #5 $189.28   5.327%   $199.3629   $199.36   $199.35   $199.40  
  Purchase #6 $111.91   13.786%   $127.3379   $127.34   $127.35   $127.30  
  Purchase #7 $175.27   10.685%   $193.9976   $194.00   $194.00   $194.00  
  7 purchase totals = $1,064.06       $1,166.1679   $1,166.16   $1,166.20   $1,166.10