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	$38.64	8.422%	$41.8943	$41.89	$41.90	$41.90
Purchase #2	$82.55	8.558%	$89.6146	$89.61	$89.60	$89.60
Purchase #3	$28.32	5.427%	$29.8569	$29.86	$29.85	$29.90
Purchase #4	$214.47	5.150%	$225.5152	$225.52	$225.50	$225.50
Purchase #5	$9.90	10.614%	$10.9508	$10.95	$10.95	$11.00
Purchase #6	$135.62	11.394%	$151.0725	$151.07	$151.05	$151.10
Purchase #7	$112.94	6.532%	$120.3172	$120.32	$120.30	$120.30
7 purchase totals =	$622.44		$669.2215	$669.22	$669.15	$669.30