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	$77.66	3.730%	$80.5567	$80.56	$80.55	$80.60
Purchase #2	$212.57	13.263%	$240.7632	$240.76	$240.75	$240.80
Purchase #3	$15.33	12.683%	$17.2743	$17.27	$17.25	$17.30
Purchase #4	$127.38	8.450%	$138.1436	$138.14	$138.15	$138.10
Purchase #5	$113.27	8.837%	$123.2797	$123.28	$123.30	$123.30
Purchase #6	$49.59	11.646%	$55.3653	$55.37	$55.35	$55.40
Purchase #7	$106.80	4.166%	$111.2493	$111.25	$111.25	$111.20
7 purchase totals =	$702.60		$766.6321	$766.63	$766.60	$766.70