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	$13.68	10.105%	$15.0624	$15.06	$15.05	$15.10
Purchase #2	$160.38	9.289%	$175.2777	$175.28	$175.30	$175.30
Purchase #3	$209.47	11.160%	$232.8469	$232.85	$232.85	$232.80
Purchase #4	$185.57	12.347%	$208.4823	$208.48	$208.50	$208.50
Purchase #5	$137.36	6.604%	$146.4313	$146.43	$146.45	$146.40
Purchase #6	$98.71	13.112%	$111.6529	$111.65	$111.65	$111.70
Purchase #7	$229.60	3.756%	$238.2238	$238.22	$238.20	$238.20
7 purchase totals =	$1,034.77		$1,127.9773	$1,127.97	$1,128.00	$1,128.00