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	$5.45	6.132%	$5.7842	$5.78	$5.80	$5.80
Purchase #2	$98.50	9.332%	$107.692	$107.69	$107.70	$107.70
Purchase #3	$99.56	13.555%	$113.0554	$113.06	$113.05	$113.10
Purchase #4	$167.69	10.486%	$185.274	$185.27	$185.25	$185.30
Purchase #5	$240.36	3.844%	$249.5994	$249.60	$249.60	$249.60
Purchase #6	$117.79	4.434%	$123.0128	$123.01	$123.00	$123.00
Purchase #7	$141.35	7.211%	$151.5427	$151.54	$151.55	$151.50
7 purchase totals =	$870.70		$935.9605	$935.95	$935.95	$936.00