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	$159.26	13.402%	$180.604	$180.60	$180.60	$180.60
Purchase #2	$97.67	9.259%	$106.7133	$106.71	$106.70	$106.70
Purchase #3	$103.49	9.423%	$113.2419	$113.24	$113.25	$113.20
Purchase #4	$38.87	9.219%	$42.4534	$42.45	$42.45	$42.50
Purchase #5	$73.98	6.416%	$78.7266	$78.73	$78.75	$78.70
Purchase #6	$99.69	4.827%	$104.502	$104.50	$104.50	$104.50
Purchase #7	$48.96	4.493%	$51.1598	$51.16	$51.15	$51.20
7 purchase totals =	$621.92		$677.4010	$677.39	$677.40	$677.40