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	$248.88	4.120%	$259.1339	$259.13	$259.15	$259.10
Purchase #2	$85.41	13.211%	$96.6935	$96.69	$96.70	$96.70
Purchase #3	$49.58	8.168%	$53.6297	$53.63	$53.65	$53.60
Purchase #4	$39.52	4.106%	$41.1427	$41.14	$41.15	$41.10
Purchase #5	$100.53	10.501%	$111.0867	$111.09	$111.10	$111.10
Purchase #6	$57.33	5.493%	$60.4791	$60.48	$60.50	$60.50
Purchase #7	$187.49	12.290%	$210.5325	$210.53	$210.55	$210.50
7 purchase totals =	$768.74		$832.6981	$832.69	$832.80	$832.60