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 $168.42   8.662%   $183.0085   $183.01   $183.00   $183.00  
  Purchase #2 $211.64   12.404%   $237.8918   $237.89   $237.90   $237.90  
  Purchase #3 $188.88   3.378%   $195.2604   $195.26   $195.25   $195.30  
  Purchase #4 $241.81   8.538%   $262.4557   $262.46   $262.45   $262.50  
  Purchase #5 $33.47   8.303%   $36.249   $36.25   $36.25   $36.20  
  Purchase #6 $126.69   8.745%   $137.769   $137.77   $137.75   $137.80  
  Purchase #7 $59.29   11.839%   $66.3093   $66.31   $66.30   $66.30  
  7 purchase totals = $1,030.20       $1,118.9437   $1,118.95   $1,118.90   $1,119.00