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	$33.99	10.380%	$37.5182	$37.52	$37.50	$37.50
Purchase #2	$29.40	9.360%	$32.1518	$32.15	$32.15	$32.20
Purchase #3	$46.33	4.789%	$48.5487	$48.55	$48.55	$48.50
Purchase #4	$66.47	13.437%	$75.4016	$75.40	$75.40	$75.40
Purchase #5	$101.54	3.776%	$105.3742	$105.37	$105.35	$105.40
Purchase #6	$103.57	3.529%	$107.225	$107.23	$107.25	$107.20
Purchase #7	$158.56	5.585%	$167.4156	$167.42	$167.40	$167.40
7 purchase totals =	$539.86		$573.6351	$573.64	$573.60	$573.60