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	$137.75	5.452%	$145.2601	$145.26	$145.25	$145.30
Purchase #2	$226.99	6.145%	$240.9385	$240.94	$240.95	$240.90
Purchase #3	$62.74	11.571%	$69.9996	$70.00	$70.00	$70.00
Purchase #4	$130.90	12.873%	$147.7508	$147.75	$147.75	$147.80
Purchase #5	$153.77	12.580%	$173.1143	$173.11	$173.10	$173.10
Purchase #6	$115.56	10.639%	$127.8544	$127.85	$127.85	$127.90
Purchase #7	$165.69	9.492%	$181.4173	$181.42	$181.40	$181.40
7 purchase totals =	$993.40		$1,086.3350	$1,086.33	$1,086.30	$1,086.40