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	$224.42	13.577%	$254.8895	$254.89	$254.90	$254.90
Purchase #2	$224.66	6.619%	$239.5302	$239.53	$239.55	$239.50
Purchase #3	$73.66	13.604%	$83.6807	$83.68	$83.70	$83.70
Purchase #4	$113.69	12.152%	$127.5056	$127.51	$127.50	$127.50
Purchase #5	$138.36	9.181%	$151.0628	$151.06	$151.05	$151.10
Purchase #6	$78.49	7.336%	$84.248	$84.25	$84.25	$84.20
Purchase #7	$33.45	13.609%	$38.0022	$38.00	$38.00	$38.00
7 purchase totals =	$886.73		$978.9190	$978.92	$978.95	$978.90