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	$159.48	4.235%	$166.234	$166.23	$166.25	$166.20
Purchase #2	$60.90	9.176%	$66.4882	$66.49	$66.50	$66.50
Purchase #3	$79.88	13.196%	$90.421	$90.42	$90.40	$90.40
Purchase #4	$32.89	3.639%	$34.0869	$34.09	$34.10	$34.10
Purchase #5	$121.63	11.678%	$135.834	$135.83	$135.85	$135.80
Purchase #6	$121.39	4.653%	$127.0383	$127.04	$127.05	$127.00
Purchase #7	$124.81	5.740%	$131.9741	$131.97	$131.95	$132.00
7 purchase totals =	$700.98		$752.0765	$752.07	$752.10	$752.00