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	$72.91	10.546%	$80.5991	$80.60	$80.60	$80.60
Purchase #2	$55.88	8.191%	$60.4571	$60.46	$60.45	$60.50
Purchase #3	$220.42	13.324%	$249.7888	$249.79	$249.80	$249.80
Purchase #4	$62.45	8.102%	$67.5097	$67.51	$67.50	$67.50
Purchase #5	$132.90	8.658%	$144.4065	$144.41	$144.40	$144.40
Purchase #6	$73.80	9.602%	$80.8863	$80.89	$80.90	$80.90
Purchase #7	$181.62	3.852%	$188.616	$188.62	$188.60	$188.60
7 purchase totals =	$799.98		$872.2635	$872.28	$872.25	$872.30