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	$96.36	12.457%	$108.3636	$108.36	$108.35	$108.40
Purchase #2	$28.84	3.461%	$29.8382	$29.84	$29.85	$29.80
Purchase #3	$80.59	10.774%	$89.2728	$89.27	$89.25	$89.30
Purchase #4	$158.37	5.241%	$166.6702	$166.67	$166.65	$166.70
Purchase #5	$174.83	12.497%	$196.6785	$196.68	$196.70	$196.70
Purchase #6	$120.88	8.210%	$130.8042	$130.80	$130.80	$130.80
Purchase #7	$128.85	12.149%	$144.504	$144.50	$144.50	$144.50
7 purchase totals =	$788.72		$866.1315	$866.12	$866.10	$866.20