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	$47.85	11.407%	$53.3082	$53.31	$53.30	$53.30
Purchase #2	$173.54	4.696%	$181.6894	$181.69	$181.70	$181.70
Purchase #3	$12.68	9.209%	$13.8477	$13.85	$13.85	$13.80
Purchase #4	$214.77	3.126%	$221.4837	$221.48	$221.50	$221.50
Purchase #5	$135.81	7.377%	$145.8287	$145.83	$145.85	$145.80
Purchase #6	$238.99	4.643%	$250.0863	$250.09	$250.10	$250.10
Purchase #7	$244.78	8.194%	$264.8373	$264.84	$264.85	$264.80
7 purchase totals =	$1,068.42		$1,131.0813	$1,131.09	$1,131.15	$1,131.00