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	$183.37	5.398%	$193.2683	$193.27	$193.25	$193.30
Purchase #2	$155.56	13.277%	$176.2137	$176.21	$176.20	$176.20
Purchase #3	$81.60	4.869%	$85.5731	$85.57	$85.55	$85.60
Purchase #4	$217.72	11.470%	$242.6925	$242.69	$242.70	$242.70
Purchase #5	$146.26	8.280%	$158.3703	$158.37	$158.35	$158.40
Purchase #6	$118.71	4.779%	$124.3832	$124.38	$124.40	$124.40
Purchase #7	$86.64	3.688%	$89.8353	$89.84	$89.85	$89.80
7 purchase totals =	$989.86		$1,070.3364	$1,070.33	$1,070.30	$1,070.40