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	$160.40	12.209%	$179.9832	$179.98	$180.00	$180.00
Purchase #2	$13.74	5.813%	$14.5387	$14.54	$14.55	$14.50
Purchase #3	$66.29	3.398%	$68.5425	$68.54	$68.55	$68.50
Purchase #4	$78.85	13.681%	$89.6375	$89.64	$89.65	$89.60
Purchase #5	$24.48	10.819%	$27.1285	$27.13	$27.15	$27.10
Purchase #6	$63.78	12.852%	$71.977	$71.98	$72.00	$72.00
Purchase #7	$64.35	9.688%	$70.5842	$70.58	$70.60	$70.60
7 purchase totals =	$471.89		$522.3916	$522.39	$522.50	$522.30