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	$25.77	4.838%	$27.0168	$27.02	$27.00	$27.00
Purchase #2	$138.32	5.353%	$145.7243	$145.72	$145.70	$145.70
Purchase #3	$78.78	10.286%	$86.8833	$86.88	$86.90	$86.90
Purchase #4	$128.28	10.308%	$141.5031	$141.50	$141.50	$141.50
Purchase #5	$173.50	10.573%	$191.8442	$191.84	$191.85	$191.80
Purchase #6	$115.74	10.174%	$127.5154	$127.52	$127.50	$127.50
Purchase #7	$97.63	3.290%	$100.842	$100.84	$100.85	$100.80
7 purchase totals =	$758.02		$821.3291	$821.32	$821.30	$821.20