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	$87.34	3.234%	$90.1646	$90.16	$90.15	$90.20
Purchase #2	$127.49	11.736%	$142.4522	$142.45	$142.45	$142.50
Purchase #3	$249.78	12.680%	$281.4521	$281.45	$281.45	$281.50
Purchase #4	$11.44	8.868%	$12.4545	$12.45	$12.45	$12.50
Purchase #5	$113.79	3.585%	$117.8694	$117.87	$117.85	$117.90
Purchase #6	$41.49	5.624%	$43.8234	$43.82	$43.80	$43.80
Purchase #7	$148.79	12.503%	$167.3932	$167.39	$167.40	$167.40
7 purchase totals =	$780.12		$855.6094	$855.59	$855.55	$855.80