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	$156.77	7.715%	$168.8648	$168.86	$168.85	$168.90
Purchase #2	$133.85	6.639%	$142.7363	$142.74	$142.75	$142.70
Purchase #3	$201.92	10.370%	$222.8591	$222.86	$222.85	$222.90
Purchase #4	$98.72	13.712%	$112.2565	$112.26	$112.25	$112.30
Purchase #5	$209.46	10.322%	$231.0805	$231.08	$231.10	$231.10
Purchase #6	$250.72	6.468%	$266.9366	$266.94	$266.95	$266.90
Purchase #7	$249.56	9.406%	$273.0336	$273.03	$273.05	$273.00
7 purchase totals =	$1,301.00		$1,417.7674	$1,417.77	$1,417.80	$1,417.80