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	$162.99	7.128%	$174.6079	$174.61	$174.60	$174.60
Purchase #2	$165.78	8.587%	$180.0155	$180.02	$180.00	$180.00
Purchase #3	$146.29	6.738%	$156.147	$156.15	$156.15	$156.10
Purchase #4	$100.94	7.697%	$108.7094	$108.71	$108.70	$108.70
Purchase #5	$36.39	11.283%	$40.4959	$40.50	$40.50	$40.50
Purchase #6	$15.82	9.251%	$17.2835	$17.28	$17.30	$17.30
Purchase #7	$111.86	10.299%	$123.3805	$123.38	$123.40	$123.40
7 purchase totals =	$740.07		$800.6397	$800.65	$800.65	$800.60