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	$51.35	3.225%	$53.006	$53.01	$53.00	$53.00
Purchase #2	$144.64	9.741%	$158.7294	$158.73	$158.75	$158.70
Purchase #3	$58.49	12.206%	$65.6293	$65.63	$65.65	$65.60
Purchase #4	$158.53	8.784%	$172.4553	$172.46	$172.45	$172.50
Purchase #5	$195.43	4.471%	$204.1677	$204.17	$204.15	$204.20
Purchase #6	$248.40	5.838%	$262.9016	$262.90	$262.90	$262.90
Purchase #7	$74.38	10.686%	$82.3282	$82.33	$82.35	$82.30
7 purchase totals =	$931.22		$999.2175	$999.23	$999.25	$999.20