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	$59.97	10.227%	$66.1031	$66.10	$66.10	$66.10
Purchase #2	$228.59	8.667%	$248.4019	$248.40	$248.40	$248.40
Purchase #3	$208.65	3.817%	$216.6142	$216.61	$216.60	$216.60
Purchase #4	$215.90	10.647%	$238.8869	$238.89	$238.90	$238.90
Purchase #5	$90.64	9.666%	$99.4013	$99.40	$99.40	$99.40
Purchase #6	$69.65	12.592%	$78.4203	$78.42	$78.40	$78.40
Purchase #7	$146.57	4.225%	$152.7626	$152.76	$152.75	$152.80
7 purchase totals =	$1,019.97		$1,100.5903	$1,100.58	$1,100.55	$1,100.60