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	$83.95	7.741%	$90.4486	$90.45	$90.45	$90.40
Purchase #2	$172.78	10.599%	$191.093	$191.09	$191.10	$191.10
Purchase #3	$78.97	4.280%	$82.3499	$82.35	$82.35	$82.30
Purchase #4	$173.34	8.312%	$187.748	$187.75	$187.75	$187.70
Purchase #5	$134.72	11.870%	$150.7113	$150.71	$150.70	$150.70
Purchase #6	$31.51	5.819%	$33.3436	$33.34	$33.35	$33.30
Purchase #7	$107.65	6.578%	$114.7312	$114.73	$114.75	$114.70
7 purchase totals =	$782.92		$850.4256	$850.42	$850.45	$850.20