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	$83.41	8.634%	$90.6116	$90.61	$90.60	$90.60
Purchase #2	$73.28	6.209%	$77.83	$77.83	$77.85	$77.80
Purchase #3	$184.99	9.563%	$202.6806	$202.68	$202.70	$202.70
Purchase #4	$13.96	5.723%	$14.7589	$14.76	$14.75	$14.80
Purchase #5	$57.41	11.764%	$64.1637	$64.16	$64.15	$64.20
Purchase #6	$105.81	6.288%	$112.4633	$112.46	$112.45	$112.50
Purchase #7	$72.47	7.711%	$78.0582	$78.06	$78.05	$78.10
7 purchase totals =	$591.33		$640.5663	$640.56	$640.55	$640.70