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	$29.40	12.817%	$33.1682	$33.17	$33.15	$33.20
Purchase #2	$146.31	8.584%	$158.8693	$158.87	$158.85	$158.90
Purchase #3	$164.56	11.816%	$184.0044	$184.00	$184.00	$184.00
Purchase #4	$68.86	13.716%	$78.3048	$78.30	$78.30	$78.30
Purchase #5	$105.30	9.117%	$114.9002	$114.90	$114.90	$114.90
Purchase #6	$171.75	7.424%	$184.5007	$184.50	$184.50	$184.50
Purchase #7	$86.95	3.156%	$89.6941	$89.69	$89.70	$89.70
7 purchase totals =	$773.13		$843.4417	$843.43	$843.40	$843.50