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	$72.29	6.385%	$76.9057	$76.91	$76.90	$76.90
Purchase #2	$101.42	11.691%	$113.277	$113.28	$113.30	$113.30
Purchase #3	$233.29	10.818%	$258.5273	$258.53	$258.55	$258.50
Purchase #4	$9.87	6.765%	$10.5377	$10.54	$10.55	$10.50
Purchase #5	$176.45	11.487%	$196.7188	$196.72	$196.70	$196.70
Purchase #6	$107.78	3.329%	$111.368	$111.37	$111.35	$111.40
Purchase #7	$14.91	5.220%	$15.6883	$15.69	$15.70	$15.70
7 purchase totals =	$716.01		$783.0228	$783.04	$783.05	$783.00