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	$164.63	3.558%	$170.4875	$170.49	$170.50	$170.50
Purchase #2	$184.90	10.394%	$204.1185	$204.12	$204.10	$204.10
Purchase #3	$70.45	11.262%	$78.3841	$78.38	$78.40	$78.40
Purchase #4	$53.74	10.195%	$59.2188	$59.22	$59.20	$59.20
Purchase #5	$89.86	6.384%	$95.5967	$95.60	$95.60	$95.60
Purchase #6	$135.81	6.604%	$144.7789	$144.78	$144.80	$144.80
Purchase #7	$157.90	11.579%	$176.1832	$176.18	$176.20	$176.20
7 purchase totals =	$857.29		$928.7677	$928.77	$928.80	$928.80