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	$90.85	7.551%	$97.7101	$97.71	$97.70	$97.70
Purchase #2	$151.94	4.588%	$158.911	$158.91	$158.90	$158.90
Purchase #3	$168.83	8.259%	$182.7737	$182.77	$182.75	$182.80
Purchase #4	$83.74	8.466%	$90.8294	$90.83	$90.85	$90.80
Purchase #5	$135.46	8.815%	$147.4008	$147.40	$147.40	$147.40
Purchase #6	$42.46	6.325%	$45.1456	$45.15	$45.15	$45.10
Purchase #7	$132.95	5.693%	$140.5188	$140.52	$140.50	$140.50
7 purchase totals =	$806.23		$863.2894	$863.29	$863.25	$863.20