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	$242.78	12.683%	$273.5718	$273.57	$273.55	$273.60
Purchase #2	$99.47	12.142%	$111.5476	$111.55	$111.55	$111.50
Purchase #3	$87.31	6.733%	$93.1886	$93.19	$93.20	$93.20
Purchase #4	$171.99	10.157%	$189.459	$189.46	$189.45	$189.50
Purchase #5	$9.77	7.198%	$10.4732	$10.47	$10.45	$10.50
Purchase #6	$134.33	11.272%	$149.4717	$149.47	$149.45	$149.50
Purchase #7	$174.62	8.821%	$190.0232	$190.02	$190.00	$190.00
7 purchase totals =	$920.27		$1,017.7351	$1,017.73	$1,017.65	$1,017.80