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	$176.83	6.831%	$188.9093	$188.91	$188.90	$188.90
Purchase #2	$208.76	9.839%	$229.2999	$229.30	$229.30	$229.30
Purchase #3	$219.55	13.845%	$249.9467	$249.95	$249.95	$249.90
Purchase #4	$199.65	5.445%	$210.5209	$210.52	$210.50	$210.50
Purchase #5	$153.74	13.274%	$174.1474	$174.15	$174.15	$174.10
Purchase #6	$157.32	7.105%	$168.4976	$168.50	$168.50	$168.50
Purchase #7	$58.83	13.797%	$66.9468	$66.95	$66.95	$66.90
7 purchase totals =	$1,174.68		$1,288.2686	$1,288.28	$1,288.25	$1,288.10