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 $83.84   3.187%   $86.512   $86.51   $86.50   $86.50  
  Purchase #2 $126.63   10.484%   $139.9059   $139.91   $139.90   $139.90  
  Purchase #3 $198.41   11.543%   $221.3125   $221.31   $221.30   $221.30  
  Purchase #4 $232.37   11.226%   $258.4559   $258.46   $258.45   $258.50  
  Purchase #5 $165.90   9.819%   $182.1897   $182.19   $182.20   $182.20  
  Purchase #6 $156.87   6.770%   $167.4901   $167.49   $167.50   $167.50  
  Purchase #7 $98.98   11.664%   $110.525   $110.53   $110.55   $110.50  
  7 purchase totals = $1,063.00       $1,166.3911   $1,166.40   $1,166.40   $1,166.40