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	$74.34	4.603%	$77.7619	$77.76	$77.75	$77.80
Purchase #2	$245.37	13.507%	$278.5121	$278.51	$278.50	$278.50
Purchase #3	$85.33	5.718%	$90.2092	$90.21	$90.20	$90.20
Purchase #4	$148.82	6.555%	$158.5752	$158.58	$158.60	$158.60
Purchase #5	$130.34	8.267%	$141.1152	$141.12	$141.10	$141.10
Purchase #6	$110.59	5.423%	$116.5873	$116.59	$116.60	$116.60
Purchase #7	$249.95	13.422%	$283.4983	$283.50	$283.50	$283.50
7 purchase totals =	$1,044.74		$1,146.2592	$1,146.27	$1,146.25	$1,146.30