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	$102.46	8.599%	$111.2705	$111.27	$111.25	$111.30
Purchase #2	$171.39	4.149%	$178.501	$178.50	$178.50	$178.50
Purchase #3	$7.41	6.836%	$7.9165	$7.92	$7.90	$7.90
Purchase #4	$75.64	6.386%	$80.4704	$80.47	$80.45	$80.50
Purchase #5	$111.35	4.644%	$116.5211	$116.52	$116.50	$116.50
Purchase #6	$214.38	12.796%	$241.8121	$241.81	$241.80	$241.80
Purchase #7	$174.80	5.345%	$184.1431	$184.14	$184.15	$184.10
7 purchase totals =	$857.43		$920.6347	$920.63	$920.55	$920.60