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 $98.61   9.194%   $107.6762   $107.68   $107.70   $107.70  
  Purchase #2 $218.31   11.190%   $242.7389   $242.74   $242.75   $242.70  
  Purchase #3 $245.44   5.460%   $258.841   $258.84   $258.85   $258.80  
  Purchase #4 $149.43   3.373%   $154.4703   $154.47   $154.45   $154.50  
  Purchase #5 $227.69   5.554%   $240.3359   $240.34   $240.35   $240.30  
  Purchase #6 $175.78   4.656%   $183.9643   $183.96   $183.95   $184.00  
  Purchase #7 $124.67   11.727%   $139.2901   $139.29   $139.30   $139.30  
  7 purchase totals = $1,239.93       $1,327.3167   $1,327.32   $1,327.35   $1,327.30