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	$91.59	13.752%	$104.1855	$104.19	$104.20	$104.20
Purchase #2	$226.67	13.144%	$256.4635	$256.46	$256.45	$256.50
Purchase #3	$19.52	13.873%	$22.228	$22.23	$22.25	$22.20
Purchase #4	$82.76	7.799%	$89.2145	$89.21	$89.20	$89.20
Purchase #5	$242.32	4.182%	$252.4538	$252.45	$252.45	$252.50
Purchase #6	$229.90	11.501%	$256.3408	$256.34	$256.35	$256.30
Purchase #7	$10.34	5.383%	$10.8966	$10.90	$10.90	$10.90
7 purchase totals =	$903.10		$991.7827	$991.78	$991.80	$991.80