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	$205.41	5.778%	$217.2786	$217.28	$217.30	$217.30
Purchase #2	$162.51	6.654%	$173.3234	$173.32	$173.30	$173.30
Purchase #3	$116.86	11.824%	$130.6775	$130.68	$130.70	$130.70
Purchase #4	$125.94	3.580%	$130.4487	$130.45	$130.45	$130.40
Purchase #5	$236.92	11.772%	$264.8102	$264.81	$264.80	$264.80
Purchase #6	$219.96	3.872%	$228.4769	$228.48	$228.50	$228.50
Purchase #7	$33.30	6.758%	$35.5504	$35.55	$35.55	$35.60
7 purchase totals =	$1,100.90		$1,180.5657	$1,180.57	$1,180.60	$1,180.60