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	$220.63	12.301%	$247.7697	$247.77	$247.75	$247.80
Purchase #2	$190.52	10.595%	$210.7056	$210.71	$210.70	$210.70
Purchase #3	$82.31	5.535%	$86.8659	$86.87	$86.85	$86.90
Purchase #4	$208.77	9.768%	$229.1627	$229.16	$229.15	$229.20
Purchase #5	$81.87	10.278%	$90.2846	$90.28	$90.30	$90.30
Purchase #6	$90.47	4.159%	$94.2326	$94.23	$94.25	$94.20
Purchase #7	$95.54	12.383%	$107.3707	$107.37	$107.35	$107.40
7 purchase totals =	$970.11		$1,066.3918	$1,066.39	$1,066.35	$1,066.50