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	$204.43	5.420%	$215.5101	$215.51	$215.50	$215.50
Purchase #2	$141.37	11.247%	$157.2699	$157.27	$157.25	$157.30
Purchase #3	$175.82	9.714%	$192.8992	$192.90	$192.90	$192.90
Purchase #4	$80.73	3.700%	$83.717	$83.72	$83.70	$83.70
Purchase #5	$26.41	3.810%	$27.4162	$27.42	$27.40	$27.40
Purchase #6	$141.91	10.488%	$156.7935	$156.79	$156.80	$156.80
Purchase #7	$97.51	11.579%	$108.8007	$108.80	$108.80	$108.80
7 purchase totals =	$868.18		$942.4066	$942.41	$942.35	$942.40