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	$69.28	7.863%	$74.7275	$74.73	$74.75	$74.70
Purchase #2	$83.66	8.227%	$90.5427	$90.54	$90.55	$90.50
Purchase #3	$55.75	13.728%	$63.4034	$63.40	$63.40	$63.40
Purchase #4	$228.98	12.731%	$258.1314	$258.13	$258.15	$258.10
Purchase #5	$53.67	10.584%	$59.3504	$59.35	$59.35	$59.40
Purchase #6	$106.60	4.149%	$111.0228	$111.02	$111.00	$111.00
Purchase #7	$72.35	10.182%	$79.7167	$79.72	$79.70	$79.70
7 purchase totals =	$670.29		$736.8949	$736.89	$736.90	$736.80