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	$66.42	10.828%	$73.612	$73.61	$73.60	$73.60
Purchase #2	$145.27	13.390%	$164.7217	$164.72	$164.70	$164.70
Purchase #3	$196.85	13.702%	$223.8224	$223.82	$223.80	$223.80
Purchase #4	$89.47	4.793%	$93.7583	$93.76	$93.75	$93.80
Purchase #5	$95.40	9.451%	$104.4163	$104.42	$104.40	$104.40
Purchase #6	$191.76	12.616%	$215.9524	$215.95	$215.95	$216.00
Purchase #7	$21.47	8.618%	$23.3203	$23.32	$23.30	$23.30
7 purchase totals =	$806.64		$899.6034	$899.60	$899.50	$899.60