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	$20.61	4.150%	$21.4653	$21.47	$21.45	$21.50
Purchase #2	$74.38	7.850%	$80.2188	$80.22	$80.20	$80.20
Purchase #3	$71.73	9.349%	$78.436	$78.44	$78.45	$78.40
Purchase #4	$36.42	3.663%	$37.7541	$37.75	$37.75	$37.80
Purchase #5	$9.45	6.155%	$10.0316	$10.03	$10.05	$10.00
Purchase #6	$131.32	7.684%	$141.4106	$141.41	$141.40	$141.40
Purchase #7	$238.51	6.745%	$254.5975	$254.60	$254.60	$254.60
7 purchase totals =	$582.42		$623.9139	$623.92	$623.90	$623.90