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	$75.73	6.848%	$80.916	$80.92	$80.90	$80.90
Purchase #2	$168.72	11.784%	$188.602	$188.60	$188.60	$188.60
Purchase #3	$111.40	3.690%	$115.5107	$115.51	$115.50	$115.50
Purchase #4	$76.92	4.776%	$80.5937	$80.59	$80.60	$80.60
Purchase #5	$50.88	7.708%	$54.8018	$54.80	$54.80	$54.80
Purchase #6	$46.61	10.391%	$51.4532	$51.45	$51.45	$51.50
Purchase #7	$133.45	3.708%	$138.3983	$138.40	$138.40	$138.40
7 purchase totals =	$663.71		$710.2757	$710.27	$710.25	$710.30