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	$75.71	4.324%	$78.9837	$78.98	$79.00	$79.00
Purchase #2	$106.89	4.354%	$111.544	$111.54	$111.55	$111.50
Purchase #3	$27.88	12.776%	$31.4419	$31.44	$31.45	$31.40
Purchase #4	$10.25	13.460%	$11.6297	$11.63	$11.65	$11.60
Purchase #5	$103.78	6.794%	$110.8308	$110.83	$110.85	$110.80
Purchase #6	$154.44	7.284%	$165.6894	$165.69	$165.70	$165.70
Purchase #7	$248.52	9.152%	$271.2646	$271.26	$271.25	$271.30
7 purchase totals =	$727.47		$781.3841	$781.37	$781.45	$781.30