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	$46.75	5.248%	$49.2034	$49.20	$49.20	$49.20
Purchase #2	$70.51	3.449%	$72.9419	$72.94	$72.95	$72.90
Purchase #3	$156.27	10.248%	$172.2845	$172.28	$172.30	$172.30
Purchase #4	$128.30	10.591%	$141.8883	$141.89	$141.90	$141.90
Purchase #5	$44.40	11.692%	$49.5912	$49.59	$49.60	$49.60
Purchase #6	$158.53	12.801%	$178.8234	$178.82	$178.80	$178.80
Purchase #7	$152.75	5.496%	$161.1451	$161.15	$161.15	$161.10
7 purchase totals =	$757.51		$825.8778	$825.87	$825.90	$825.80