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	$230.68	13.335%	$261.4412	$261.44	$261.45	$261.40
Purchase #2	$98.41	13.356%	$111.5536	$111.55	$111.55	$111.60
Purchase #3	$220.74	12.320%	$247.9352	$247.94	$247.95	$247.90
Purchase #4	$244.45	10.474%	$270.0537	$270.05	$270.05	$270.10
Purchase #5	$93.94	4.844%	$98.4905	$98.49	$98.50	$98.50
Purchase #6	$115.78	9.752%	$127.0709	$127.07	$127.05	$127.10
Purchase #7	$62.46	4.437%	$65.2314	$65.23	$65.25	$65.20
7 purchase totals =	$1,066.46		$1,181.7765	$1,181.77	$1,181.80	$1,181.80