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	$30.73	8.107%	$33.2213	$33.22	$33.20	$33.20
Purchase #2	$137.46	4.145%	$143.1577	$143.16	$143.15	$143.20
Purchase #3	$174.69	12.343%	$196.252	$196.25	$196.25	$196.30
Purchase #4	$118.70	9.702%	$130.2163	$130.22	$130.20	$130.20
Purchase #5	$176.29	6.118%	$187.0754	$187.08	$187.10	$187.10
Purchase #6	$129.98	12.836%	$146.6642	$146.66	$146.65	$146.70
Purchase #7	$232.31	13.600%	$263.9042	$263.90	$263.90	$263.90
7 purchase totals =	$1,000.16		$1,100.4911	$1,100.49	$1,100.45	$1,100.60