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	$36.28	10.719%	$40.1689	$40.17	$40.15	$40.20
Purchase #2	$89.87	10.701%	$99.487	$99.49	$99.50	$99.50
Purchase #3	$247.76	10.301%	$273.2818	$273.28	$273.30	$273.30
Purchase #4	$171.36	12.313%	$192.4596	$192.46	$192.45	$192.50
Purchase #5	$81.94	8.212%	$88.6689	$88.67	$88.65	$88.70
Purchase #6	$56.98	10.561%	$62.9977	$63.00	$63.00	$63.00
Purchase #7	$107.90	3.123%	$111.2697	$111.27	$111.25	$111.30
7 purchase totals =	$792.09		$868.3336	$868.34	$868.30	$868.50