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	$72.52	7.732%	$78.1272	$78.13	$78.15	$78.10
Purchase #2	$83.28	13.727%	$94.7118	$94.71	$94.70	$94.70
Purchase #3	$83.42	6.758%	$89.0575	$89.06	$89.05	$89.10
Purchase #4	$216.49	8.119%	$234.0668	$234.07	$234.05	$234.10
Purchase #5	$56.97	9.848%	$62.5804	$62.58	$62.60	$62.60
Purchase #6	$18.52	11.301%	$20.6129	$20.61	$20.60	$20.60
Purchase #7	$26.94	10.295%	$29.7135	$29.71	$29.70	$29.70
7 purchase totals =	$558.14		$608.8701	$608.87	$608.85	$608.90