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	$50.72	3.698%	$52.5956	$52.60	$52.60	$52.60
Purchase #2	$200.77	10.195%	$221.2385	$221.24	$221.25	$221.20
Purchase #3	$86.71	6.221%	$92.1042	$92.10	$92.10	$92.10
Purchase #4	$90.51	13.722%	$102.9298	$102.93	$102.95	$102.90
Purchase #5	$28.84	11.495%	$32.1552	$32.16	$32.15	$32.20
Purchase #6	$121.89	4.389%	$127.2398	$127.24	$127.25	$127.20
Purchase #7	$28.64	9.831%	$31.4556	$31.46	$31.45	$31.50
7 purchase totals =	$608.08		$659.7187	$659.73	$659.75	$659.70