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 $83.74   3.610%   $86.763   $86.76   $86.75   $86.80  
  Purchase #2 $109.70   8.195%   $118.6899   $118.69   $118.70   $118.70  
  Purchase #3 $117.80   8.605%   $127.9367   $127.94   $127.95   $127.90  
  Purchase #4 $148.45   12.312%   $166.7272   $166.73   $166.75   $166.70  
  Purchase #5 $41.95   9.577%   $45.9676   $45.97   $45.95   $46.00  
  Purchase #6 $199.35   8.164%   $215.6249   $215.62   $215.60   $215.60  
  Purchase #7 $127.59   4.300%   $133.0764   $133.08   $133.10   $133.10  
  7 purchase totals = $828.58       $894.7857   $894.79   $894.80   $894.80