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	$53.90	3.759%	$55.9261	$55.93	$55.95	$55.90
Purchase #2	$248.45	13.733%	$282.5696	$282.57	$282.55	$282.60
Purchase #3	$193.31	9.404%	$211.4889	$211.49	$211.50	$211.50
Purchase #4	$231.83	5.819%	$245.3202	$245.32	$245.30	$245.30
Purchase #5	$228.52	5.565%	$241.2371	$241.24	$241.25	$241.20
Purchase #6	$82.83	9.106%	$90.3725	$90.37	$90.35	$90.40
Purchase #7	$138.76	3.430%	$143.5195	$143.52	$143.50	$143.50
7 purchase totals =	$1,177.60		$1,270.4339	$1,270.44	$1,270.40	$1,270.40