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	$84.88	6.405%	$90.3166	$90.32	$90.30	$90.30
Purchase #2	$166.82	6.848%	$178.2438	$178.24	$178.25	$178.20
Purchase #3	$5.33	9.346%	$5.8281	$5.83	$5.85	$5.80
Purchase #4	$115.33	13.222%	$130.5789	$130.58	$130.60	$130.60
Purchase #5	$77.85	6.219%	$82.6915	$82.69	$82.70	$82.70
Purchase #6	$66.32	3.684%	$68.7632	$68.76	$68.75	$68.80
Purchase #7	$238.90	10.491%	$263.963	$263.96	$263.95	$264.00
7 purchase totals =	$755.43		$820.3851	$820.38	$820.40	$820.40