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	$56.85	8.572%	$61.7232	$61.72	$61.70	$61.70
Purchase #2	$174.80	6.560%	$186.2669	$186.27	$186.25	$186.30
Purchase #3	$86.53	3.702%	$89.7333	$89.73	$89.75	$89.70
Purchase #4	$69.65	5.232%	$73.2941	$73.29	$73.30	$73.30
Purchase #5	$143.25	10.841%	$158.7797	$158.78	$158.80	$158.80
Purchase #6	$149.31	12.651%	$168.1992	$168.20	$168.20	$168.20
Purchase #7	$239.37	6.699%	$255.4054	$255.41	$255.40	$255.40
7 purchase totals =	$919.76		$993.4018	$993.40	$993.40	$993.40