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	$81.78	10.747%	$90.5689	$90.57	$90.55	$90.60
Purchase #2	$13.53	11.293%	$15.0579	$15.06	$15.05	$15.10
Purchase #3	$125.36	11.229%	$139.4367	$139.44	$139.45	$139.40
Purchase #4	$50.54	5.162%	$53.1489	$53.15	$53.15	$53.10
Purchase #5	$83.32	12.545%	$93.7725	$93.77	$93.75	$93.80
Purchase #6	$88.93	10.104%	$97.9155	$97.92	$97.90	$97.90
Purchase #7	$105.60	6.401%	$112.3595	$112.36	$112.35	$112.40
7 purchase totals =	$549.06		$602.2599	$602.27	$602.20	$602.30