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	$99.52	3.699%	$103.2012	$103.20	$103.20	$103.20
Purchase #2	$35.63	13.390%	$40.4009	$40.40	$40.40	$40.40
Purchase #3	$114.26	11.533%	$127.4376	$127.44	$127.45	$127.40
Purchase #4	$183.53	7.612%	$197.5003	$197.50	$197.50	$197.50
Purchase #5	$73.33	6.449%	$78.0591	$78.06	$78.05	$78.10
Purchase #6	$100.76	11.534%	$112.3817	$112.38	$112.40	$112.40
Purchase #7	$184.92	13.296%	$209.507	$209.51	$209.50	$209.50
7 purchase totals =	$791.95		$868.4878	$868.49	$868.50	$868.50