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	$170.58	8.801%	$185.5927	$185.59	$185.60	$185.60
Purchase #2	$79.46	5.359%	$83.7183	$83.72	$83.70	$83.70
Purchase #3	$86.38	12.816%	$97.4505	$97.45	$97.45	$97.50
Purchase #4	$159.64	8.321%	$172.9236	$172.92	$172.90	$172.90
Purchase #5	$172.36	8.537%	$187.0744	$187.07	$187.05	$187.10
Purchase #6	$33.67	13.711%	$38.2865	$38.29	$38.30	$38.30
Purchase #7	$33.85	11.621%	$37.7837	$37.78	$37.80	$37.80
7 purchase totals =	$735.94		$802.8297	$802.82	$802.80	$802.90