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	$145.56	4.134%	$151.5775	$151.58	$151.60	$151.60
Purchase #2	$129.97	10.861%	$144.086	$144.09	$144.10	$144.10
Purchase #3	$148.45	6.119%	$157.5337	$157.53	$157.55	$157.50
Purchase #4	$73.83	5.438%	$77.8449	$77.84	$77.85	$77.80
Purchase #5	$31.68	6.785%	$33.8295	$33.83	$33.85	$33.80
Purchase #6	$124.75	13.334%	$141.3842	$141.38	$141.40	$141.40
Purchase #7	$110.32	12.531%	$124.1442	$124.14	$124.15	$124.10
7 purchase totals =	$764.56		$830.4000	$830.39	$830.50	$830.30