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	$37.67	3.158%	$38.8596	$38.86	$38.85	$38.90
Purchase #2	$137.72	5.413%	$145.1748	$145.17	$145.15	$145.20
Purchase #3	$231.57	6.502%	$246.6267	$246.63	$246.65	$246.60
Purchase #4	$118.68	7.753%	$127.8813	$127.88	$127.90	$127.90
Purchase #5	$183.36	5.816%	$194.0242	$194.02	$194.00	$194.00
Purchase #6	$66.98	8.158%	$72.4442	$72.44	$72.45	$72.40
Purchase #7	$226.83	12.180%	$254.4579	$254.46	$254.45	$254.50
7 purchase totals =	$1,002.81		$1,079.4687	$1,079.46	$1,079.45	$1,079.50