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	$80.83	12.500%	$90.9338	$90.93	$90.95	$90.90
Purchase #2	$80.92	10.582%	$89.483	$89.48	$89.50	$89.50
Purchase #3	$186.90	7.702%	$201.295	$201.30	$201.30	$201.30
Purchase #4	$49.32	7.325%	$52.9327	$52.93	$52.95	$52.90
Purchase #5	$205.54	13.558%	$233.4071	$233.41	$233.40	$233.40
Purchase #6	$177.85	5.792%	$188.1511	$188.15	$188.15	$188.20
Purchase #7	$105.52	9.189%	$115.2162	$115.22	$115.20	$115.20
7 purchase totals =	$886.88		$971.4189	$971.42	$971.45	$971.40