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 $145.38   8.487%   $157.7184   $157.72   $157.70   $157.70  
  Purchase #2 $206.50   9.628%   $226.3818   $226.38   $226.40   $226.40  
  Purchase #3 $30.67   4.637%   $32.0922   $32.09   $32.10   $32.10  
  Purchase #4 $142.50   3.694%   $147.764   $147.76   $147.75   $147.80  
  Purchase #5 $21.98   7.805%   $23.6955   $23.70   $23.70   $23.70  
  Purchase #6 $132.92   7.633%   $143.0658   $143.07   $143.05   $143.10  
  Purchase #7 $185.68   10.615%   $205.3899   $205.39   $205.40   $205.40  
  7 purchase totals = $865.63       $936.1076   $936.11   $936.10   $936.20