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	$74.54	5.521%	$78.6554	$78.66	$78.65	$78.70
Purchase #2	$188.95	13.613%	$214.6718	$214.67	$214.65	$214.70
Purchase #3	$249.61	8.516%	$270.8668	$270.87	$270.85	$270.90
Purchase #4	$82.68	8.787%	$89.9451	$89.95	$89.95	$89.90
Purchase #5	$94.83	13.407%	$107.5439	$107.54	$107.55	$107.50
Purchase #6	$6.59	13.638%	$7.4887	$7.49	$7.50	$7.50
Purchase #7	$156.36	11.188%	$173.8536	$173.85	$173.85	$173.90
7 purchase totals =	$853.56		$943.0253	$943.03	$943.00	$943.10