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	$128.80	13.263%	$145.8827	$145.88	$145.90	$145.90
Purchase #2	$42.27	8.335%	$45.7932	$45.79	$45.80	$45.80
Purchase #3	$111.25	3.869%	$115.5543	$115.55	$115.55	$115.60
Purchase #4	$178.33	6.332%	$189.6219	$189.62	$189.60	$189.60
Purchase #5	$164.54	13.814%	$187.2696	$187.27	$187.25	$187.30
Purchase #6	$28.52	12.647%	$32.1269	$32.13	$32.15	$32.10
Purchase #7	$88.75	12.705%	$100.0257	$100.03	$100.05	$100.00
7 purchase totals =	$742.46		$816.2743	$816.27	$816.30	$816.30