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	$197.51	10.686%	$218.6159	$218.62	$218.60	$218.60
Purchase #2	$82.78	8.683%	$89.9678	$89.97	$89.95	$90.00
Purchase #3	$167.65	10.571%	$185.3723	$185.37	$185.35	$185.40
Purchase #4	$175.51	4.551%	$183.4975	$183.50	$183.50	$183.50
Purchase #5	$91.38	13.640%	$103.8442	$103.84	$103.85	$103.80
Purchase #6	$91.80	12.343%	$103.1309	$103.13	$103.15	$103.10
Purchase #7	$243.51	5.341%	$256.5159	$256.52	$256.50	$256.50
7 purchase totals =	$1,050.14		$1,140.9445	$1,140.95	$1,140.90	$1,140.90