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	$220.44	4.580%	$230.5362	$230.54	$230.55	$230.50
Purchase #2	$179.34	10.171%	$197.5807	$197.58	$197.60	$197.60
Purchase #3	$214.89	8.134%	$232.3692	$232.37	$232.35	$232.40
Purchase #4	$100.65	9.116%	$109.8253	$109.83	$109.85	$109.80
Purchase #5	$85.91	7.698%	$92.5234	$92.52	$92.50	$92.50
Purchase #6	$33.58	12.705%	$37.8463	$37.85	$37.85	$37.80
Purchase #7	$210.27	6.489%	$223.9144	$223.91	$223.90	$223.90
7 purchase totals =	$1,045.08		$1,124.5955	$1,124.60	$1,124.60	$1,124.50