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	$187.94	13.276%	$212.8909	$212.89	$212.90	$212.90
Purchase #2	$17.56	11.531%	$19.5848	$19.58	$19.60	$19.60
Purchase #3	$138.93	6.826%	$148.4134	$148.41	$148.40	$148.40
Purchase #4	$46.44	13.666%	$52.7865	$52.79	$52.80	$52.80
Purchase #5	$53.67	4.689%	$56.1866	$56.19	$56.20	$56.20
Purchase #6	$44.32	3.710%	$45.9643	$45.96	$45.95	$46.00
Purchase #7	$100.87	8.119%	$109.0596	$109.06	$109.05	$109.10
7 purchase totals =	$589.73		$644.8861	$644.88	$644.90	$645.00