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	$155.82	7.744%	$167.8867	$167.89	$167.90	$167.90
Purchase #2	$78.79	5.316%	$82.9785	$82.98	$83.00	$83.00
Purchase #3	$214.40	5.229%	$225.611	$225.61	$225.60	$225.60
Purchase #4	$176.26	5.451%	$185.8679	$185.87	$185.85	$185.90
Purchase #5	$141.52	11.136%	$157.2797	$157.28	$157.30	$157.30
Purchase #6	$92.70	4.267%	$96.6555	$96.66	$96.65	$96.70
Purchase #7	$196.57	13.835%	$223.7655	$223.77	$223.75	$223.80
7 purchase totals =	$1,056.06		$1,140.0448	$1,140.06	$1,140.05	$1,140.20