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	$49.50	9.398%	$54.152	$54.15	$54.15	$54.20
Purchase #2	$132.95	8.460%	$144.1976	$144.20	$144.20	$144.20
Purchase #3	$22.47	13.623%	$25.5311	$25.53	$25.55	$25.50
Purchase #4	$38.84	4.363%	$40.5346	$40.53	$40.55	$40.50
Purchase #5	$120.42	6.790%	$128.5965	$128.60	$128.60	$128.60
Purchase #6	$72.63	6.826%	$77.5877	$77.59	$77.60	$77.60
Purchase #7	$24.63	12.762%	$27.7733	$27.77	$27.75	$27.80
7 purchase totals =	$461.44		$498.3728	$498.37	$498.40	$498.40