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	$29.63	10.678%	$32.7939	$32.79	$32.80	$32.80
Purchase #2	$83.71	6.336%	$89.0139	$89.01	$89.00	$89.00
Purchase #3	$49.73	12.636%	$56.0139	$56.01	$56.00	$56.00
Purchase #4	$65.69	5.255%	$69.142	$69.14	$69.15	$69.10
Purchase #5	$193.93	12.288%	$217.7601	$217.76	$217.75	$217.80
Purchase #6	$150.35	5.624%	$158.8057	$158.81	$158.80	$158.80
Purchase #7	$48.28	11.631%	$53.8954	$53.90	$53.90	$53.90
7 purchase totals =	$621.32		$677.4249	$677.42	$677.40	$677.40