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	$204.96	11.387%	$228.2988	$228.30	$228.30	$228.30
Purchase #2	$234.45	8.288%	$253.8812	$253.88	$253.90	$253.90
Purchase #3	$21.83	13.290%	$24.7312	$24.73	$24.75	$24.70
Purchase #4	$143.93	13.174%	$162.8913	$162.89	$162.90	$162.90
Purchase #5	$144.83	3.725%	$150.2249	$150.22	$150.20	$150.20
Purchase #6	$68.71	5.406%	$72.4245	$72.42	$72.40	$72.40
Purchase #7	$164.79	5.399%	$173.687	$173.69	$173.70	$173.70
7 purchase totals =	$983.50		$1,066.1389	$1,066.13	$1,066.15	$1,066.10