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	$35.60	8.575%	$38.6527	$38.65	$38.65	$38.70
Purchase #2	$194.57	9.352%	$212.7662	$212.77	$212.75	$212.80
Purchase #3	$107.92	3.252%	$111.4296	$111.43	$111.45	$111.40
Purchase #4	$173.48	7.633%	$186.7217	$186.72	$186.70	$186.70
Purchase #5	$198.97	5.454%	$209.8218	$209.82	$209.80	$209.80
Purchase #6	$162.72	6.303%	$172.9762	$172.98	$173.00	$173.00
Purchase #7	$86.90	3.581%	$90.0119	$90.01	$90.00	$90.00
7 purchase totals =	$960.16		$1,022.3801	$1,022.38	$1,022.35	$1,022.40