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	$21.30	3.253%	$21.9929	$21.99	$22.00	$22.00
Purchase #2	$131.67	11.520%	$146.8384	$146.84	$146.85	$146.80
Purchase #3	$93.70	7.374%	$100.6094	$100.61	$100.60	$100.60
Purchase #4	$22.45	6.530%	$23.916	$23.92	$23.90	$23.90
Purchase #5	$163.87	12.870%	$184.9601	$184.96	$184.95	$185.00
Purchase #6	$118.92	7.344%	$127.6535	$127.65	$127.65	$127.70
Purchase #7	$96.32	13.229%	$109.0622	$109.06	$109.05	$109.10
7 purchase totals =	$648.23		$715.0325	$715.03	$715.00	$715.10