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	$17.99	4.664%	$18.8291	$18.83	$18.85	$18.80
Purchase #2	$51.26	8.626%	$55.6817	$55.68	$55.70	$55.70
Purchase #3	$222.93	3.309%	$230.3068	$230.31	$230.30	$230.30
Purchase #4	$76.70	12.771%	$86.4954	$86.50	$86.50	$86.50
Purchase #5	$83.41	7.229%	$89.4397	$89.44	$89.45	$89.40
Purchase #6	$83.46	8.799%	$90.8036	$90.80	$90.80	$90.80
Purchase #7	$49.94	7.783%	$53.8268	$53.83	$53.85	$53.80
7 purchase totals =	$585.69		$625.3831	$625.39	$625.45	$625.30