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 $32.81   8.590%   $35.6284   $35.63   $35.65   $35.60  
  Purchase #2 $145.87   11.737%   $162.9908   $162.99   $163.00   $163.00  
  Purchase #3 $221.99   8.594%   $241.0678   $241.07   $241.05   $241.10  
  Purchase #4 $177.78   3.293%   $183.6343   $183.63   $183.65   $183.60  
  Purchase #5 $90.94   8.397%   $98.5762   $98.58   $98.60   $98.60  
  Purchase #6 $123.49   10.484%   $136.4367   $136.44   $136.45   $136.40  
  Purchase #7 $167.37   6.223%   $177.7854   $177.79   $177.80   $177.80  
  7 purchase totals = $960.25       $1,036.1196   $1,036.13   $1,036.20   $1,036.10