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	$132.78	3.560%	$137.507	$137.51	$137.50	$137.50
Purchase #2	$126.73	5.481%	$133.6761	$133.68	$133.70	$133.70
Purchase #3	$114.80	10.693%	$127.0756	$127.08	$127.10	$127.10
Purchase #4	$98.28	11.568%	$109.649	$109.65	$109.65	$109.60
Purchase #5	$209.87	9.809%	$230.4561	$230.46	$230.45	$230.50
Purchase #6	$32.98	13.438%	$37.4119	$37.41	$37.40	$37.40
Purchase #7	$19.87	13.524%	$22.5572	$22.56	$22.55	$22.60
7 purchase totals =	$735.31		$798.3329	$798.35	$798.35	$798.40