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	$83.49	6.143%	$88.6188	$88.62	$88.60	$88.60
Purchase #2	$60.89	10.799%	$67.4655	$67.47	$67.45	$67.50
Purchase #3	$72.33	7.315%	$77.6209	$77.62	$77.60	$77.60
Purchase #4	$144.44	8.655%	$156.9413	$156.94	$156.95	$156.90
Purchase #5	$56.59	10.196%	$62.3599	$62.36	$62.35	$62.40
Purchase #6	$193.41	10.856%	$214.4066	$214.41	$214.40	$214.40
Purchase #7	$97.85	7.466%	$105.1555	$105.16	$105.15	$105.20
7 purchase totals =	$709.00		$772.5685	$772.58	$772.50	$772.60