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	$123.80	6.261%	$131.5511	$131.55	$131.55	$131.60
Purchase #2	$238.67	11.646%	$266.4655	$266.47	$266.45	$266.50
Purchase #3	$243.32	11.611%	$271.5719	$271.57	$271.55	$271.60
Purchase #4	$194.34	9.388%	$212.5846	$212.58	$212.60	$212.60
Purchase #5	$231.27	9.184%	$252.5098	$252.51	$252.50	$252.50
Purchase #6	$213.54	11.131%	$237.3091	$237.31	$237.30	$237.30
Purchase #7	$166.73	11.452%	$185.8239	$185.82	$185.80	$185.80
7 purchase totals =	$1,411.67		$1,557.8159	$1,557.81	$1,557.75	$1,557.90