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	$80.52	13.503%	$91.3926	$91.39	$91.40	$91.40
Purchase #2	$146.89	13.409%	$166.5865	$166.59	$166.60	$166.60
Purchase #3	$248.59	6.195%	$263.9902	$263.99	$264.00	$264.00
Purchase #4	$248.61	13.693%	$282.6522	$282.65	$282.65	$282.70
Purchase #5	$171.83	11.632%	$191.8173	$191.82	$191.80	$191.80
Purchase #6	$58.85	12.654%	$66.2969	$66.30	$66.30	$66.30
Purchase #7	$210.27	10.873%	$233.1327	$233.13	$233.15	$233.10
7 purchase totals =	$1,165.56		$1,295.8684	$1,295.87	$1,295.90	$1,295.90