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	$157.81	4.304%	$164.6021	$164.60	$164.60	$164.60
Purchase #2	$90.50	12.790%	$102.075	$102.08	$102.10	$102.10
Purchase #3	$67.96	9.644%	$74.5141	$74.51	$74.50	$74.50
Purchase #4	$20.35	11.130%	$22.615	$22.62	$22.60	$22.60
Purchase #5	$96.77	13.556%	$109.8881	$109.89	$109.90	$109.90
Purchase #6	$12.87	9.580%	$14.1029	$14.10	$14.10	$14.10
Purchase #7	$53.76	12.496%	$60.4778	$60.48	$60.50	$60.50
7 purchase totals =	$500.02		$548.2750	$548.28	$548.30	$548.30