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	$209.86	9.481%	$229.7568	$229.76	$229.75	$229.80
Purchase #2	$162.62	6.311%	$172.8829	$172.88	$172.90	$172.90
Purchase #3	$50.35	13.746%	$57.2711	$57.27	$57.25	$57.30
Purchase #4	$148.73	13.307%	$168.5215	$168.52	$168.50	$168.50
Purchase #5	$114.73	11.552%	$127.9836	$127.98	$128.00	$128.00
Purchase #6	$7.98	7.502%	$8.5787	$8.58	$8.60	$8.60
Purchase #7	$26.83	8.310%	$29.0596	$29.06	$29.05	$29.10
7 purchase totals =	$721.10		$794.0542	$794.05	$794.05	$794.20