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	$127.85	8.195%	$138.3273	$138.33	$138.35	$138.30
Purchase #2	$52.74	7.332%	$56.6069	$56.61	$56.60	$56.60
Purchase #3	$92.51	7.331%	$99.2919	$99.29	$99.30	$99.30
Purchase #4	$182.78	4.695%	$191.3615	$191.36	$191.35	$191.40
Purchase #5	$40.76	9.769%	$44.7418	$44.74	$44.75	$44.70
Purchase #6	$49.52	9.105%	$54.0288	$54.03	$54.05	$54.00
Purchase #7	$187.71	10.849%	$208.0747	$208.07	$208.05	$208.10
7 purchase totals =	$733.87		$792.4329	$792.43	$792.45	$792.40