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	$194.66	12.482%	$218.9575	$218.96	$218.95	$219.00
Purchase #2	$86.43	4.800%	$90.5786	$90.58	$90.60	$90.60
Purchase #3	$155.97	10.428%	$172.2346	$172.23	$172.25	$172.20
Purchase #4	$180.34	4.250%	$188.0045	$188.00	$188.00	$188.00
Purchase #5	$59.59	13.808%	$67.8182	$67.82	$67.80	$67.80
Purchase #6	$28.45	7.422%	$30.5616	$30.56	$30.55	$30.60
Purchase #7	$163.85	5.611%	$173.0436	$173.04	$173.05	$173.00
7 purchase totals =	$869.29		$941.1986	$941.19	$941.20	$941.20