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	$245.50	12.219%	$275.4976	$275.50	$275.50	$275.50
Purchase #2	$209.77	13.589%	$238.2756	$238.28	$238.30	$238.30
Purchase #3	$147.41	10.332%	$162.6404	$162.64	$162.65	$162.60
Purchase #4	$96.58	4.286%	$100.7194	$100.72	$100.70	$100.70
Purchase #5	$156.67	3.183%	$161.6568	$161.66	$161.65	$161.70
Purchase #6	$87.96	13.471%	$99.8091	$99.81	$99.80	$99.80
Purchase #7	$220.82	9.505%	$241.8089	$241.81	$241.80	$241.80
7 purchase totals =	$1,164.71		$1,280.4078	$1,280.42	$1,280.40	$1,280.40