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	$59.60	11.533%	$66.4737	$66.47	$66.45	$66.50
Purchase #2	$19.85	5.720%	$20.9854	$20.99	$21.00	$21.00
Purchase #3	$183.59	6.841%	$196.1494	$196.15	$196.15	$196.10
Purchase #4	$17.29	11.740%	$19.3198	$19.32	$19.30	$19.30
Purchase #5	$192.27	10.306%	$212.0853	$212.09	$212.10	$212.10
Purchase #6	$25.40	13.519%	$28.8338	$28.83	$28.85	$28.80
Purchase #7	$59.51	13.748%	$67.6914	$67.69	$67.70	$67.70
7 purchase totals =	$557.51		$611.5388	$611.54	$611.55	$611.50