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	$93.99	7.322%	$100.8719	$100.87	$100.85	$100.90
Purchase #2	$30.71	9.722%	$33.6956	$33.70	$33.70	$33.70
Purchase #3	$232.72	10.655%	$257.5163	$257.52	$257.50	$257.50
Purchase #4	$132.80	13.294%	$150.4544	$150.45	$150.45	$150.50
Purchase #5	$16.25	11.160%	$18.0635	$18.06	$18.05	$18.10
Purchase #6	$128.83	4.252%	$134.3079	$134.31	$134.30	$134.30
Purchase #7	$105.82	7.168%	$113.4052	$113.41	$113.40	$113.40
7 purchase totals =	$741.12		$808.3148	$808.32	$808.25	$808.40