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	$178.44	6.426%	$189.9066	$189.91	$189.90	$189.90
Purchase #2	$151.50	9.199%	$165.4365	$165.44	$165.45	$165.40
Purchase #3	$249.50	11.287%	$277.6611	$277.66	$277.65	$277.70
Purchase #4	$20.77	6.573%	$22.1352	$22.14	$22.15	$22.10
Purchase #5	$241.43	4.177%	$251.5145	$251.51	$251.50	$251.50
Purchase #6	$140.96	11.217%	$156.7715	$156.77	$156.75	$156.80
Purchase #7	$46.26	4.611%	$48.393	$48.39	$48.40	$48.40
7 purchase totals =	$1,028.86		$1,111.8184	$1,111.82	$1,111.80	$1,111.80