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	$73.83	12.373%	$82.965	$82.97	$82.95	$83.00
Purchase #2	$149.39	3.717%	$154.9428	$154.94	$154.95	$154.90
Purchase #3	$21.40	12.820%	$24.1435	$24.14	$24.15	$24.10
Purchase #4	$219.75	8.495%	$238.4178	$238.42	$238.40	$238.40
Purchase #5	$97.82	13.509%	$111.0345	$111.03	$111.05	$111.00
Purchase #6	$113.81	12.240%	$127.7403	$127.74	$127.75	$127.70
Purchase #7	$94.43	12.816%	$106.5321	$106.53	$106.55	$106.50
7 purchase totals =	$770.43		$845.7760	$845.77	$845.80	$845.60