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	$102.83	9.405%	$112.5012	$112.50	$112.50	$112.50
Purchase #2	$48.58	10.760%	$53.8072	$53.81	$53.80	$53.80
Purchase #3	$171.25	4.396%	$178.7782	$178.78	$178.80	$178.80
Purchase #4	$152.27	13.310%	$172.5371	$172.54	$172.55	$172.50
Purchase #5	$16.59	9.145%	$18.1072	$18.11	$18.10	$18.10
Purchase #6	$20.51	8.433%	$22.2396	$22.24	$22.25	$22.20
Purchase #7	$52.54	3.647%	$54.4561	$54.46	$54.45	$54.50
7 purchase totals =	$564.57		$612.4266	$612.44	$612.45	$612.40