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	$185.67	13.863%	$211.4094	$211.41	$211.40	$211.40
Purchase #2	$134.67	7.452%	$144.7056	$144.71	$144.70	$144.70
Purchase #3	$176.32	5.290%	$185.6473	$185.65	$185.65	$185.60
Purchase #4	$92.77	8.722%	$100.8614	$100.86	$100.85	$100.90
Purchase #5	$188.80	5.470%	$199.1274	$199.13	$199.15	$199.10
Purchase #6	$21.57	4.511%	$22.543	$22.54	$22.55	$22.50
Purchase #7	$115.59	10.463%	$127.6842	$127.68	$127.70	$127.70
7 purchase totals =	$915.39		$991.9783	$991.98	$992.00	$991.90