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 $119.65   3.781%   $124.174   $124.17   $124.15   $124.20  
  Purchase #2 $161.51   12.859%   $182.2786   $182.28   $182.30   $182.30  
  Purchase #3 $34.38   12.417%   $38.649   $38.65   $38.65   $38.60  
  Purchase #4 $169.64   4.161%   $176.6987   $176.70   $176.70   $176.70  
  Purchase #5 $139.36   8.758%   $151.5651   $151.57   $151.55   $151.60  
  Purchase #6 $157.70   8.502%   $171.1077   $171.11   $171.10   $171.10  
  Purchase #7 $196.77   11.771%   $219.9318   $219.93   $219.95   $219.90  
  7 purchase totals = $979.01       $1,064.4049   $1,064.41   $1,064.40   $1,064.40