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	$225.49	12.265%	$253.1463	$253.15	$253.15	$253.10
Purchase #2	$175.43	4.648%	$183.584	$183.58	$183.60	$183.60
Purchase #3	$77.59	3.731%	$80.4849	$80.48	$80.50	$80.50
Purchase #4	$104.66	11.145%	$116.3244	$116.32	$116.30	$116.30
Purchase #5	$170.64	4.382%	$178.1174	$178.12	$178.10	$178.10
Purchase #6	$100.50	3.548%	$104.0657	$104.07	$104.05	$104.10
Purchase #7	$34.46	3.106%	$35.5303	$35.53	$35.55	$35.50
7 purchase totals =	$888.77		$951.2530	$951.25	$951.25	$951.20