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	$34.58	12.139%	$38.7777	$38.78	$38.80	$38.80
Purchase #2	$56.64	6.163%	$60.1307	$60.13	$60.15	$60.10
Purchase #3	$218.61	8.666%	$237.5547	$237.55	$237.55	$237.60
Purchase #4	$209.90	13.145%	$237.4914	$237.49	$237.50	$237.50
Purchase #5	$111.72	4.595%	$116.8535	$116.85	$116.85	$116.90
Purchase #6	$123.78	11.404%	$137.8959	$137.90	$137.90	$137.90
Purchase #7	$182.62	3.445%	$188.9113	$188.91	$188.90	$188.90
7 purchase totals =	$937.85		$1,017.6152	$1,017.61	$1,017.65	$1,017.70