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	$11.33	10.697%	$12.542	$12.54	$12.55	$12.50
Purchase #2	$144.45	7.287%	$154.9761	$154.98	$155.00	$155.00
Purchase #3	$114.27	7.762%	$123.1396	$123.14	$123.15	$123.10
Purchase #4	$241.89	11.303%	$269.2308	$269.23	$269.25	$269.20
Purchase #5	$80.52	12.520%	$90.6011	$90.60	$90.60	$90.60
Purchase #6	$54.61	7.676%	$58.8019	$58.80	$58.80	$58.80
Purchase #7	$23.36	3.245%	$24.118	$24.12	$24.10	$24.10
7 purchase totals =	$670.43		$733.4095	$733.41	$733.45	$733.30