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	$197.96	8.208%	$214.2086	$214.21	$214.20	$214.20
Purchase #2	$245.26	4.347%	$255.9215	$255.92	$255.90	$255.90
Purchase #3	$42.51	3.377%	$43.9456	$43.95	$43.95	$43.90
Purchase #4	$174.65	5.379%	$184.0444	$184.04	$184.05	$184.00
Purchase #5	$33.84	9.766%	$37.1448	$37.14	$37.15	$37.10
Purchase #6	$171.33	4.767%	$179.4973	$179.50	$179.50	$179.50
Purchase #7	$56.33	13.787%	$64.0962	$64.10	$64.10	$64.10
7 purchase totals =	$921.88		$978.8584	$978.86	$978.85	$978.70