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	$53.67	8.808%	$58.3973	$58.40	$58.40	$58.40
Purchase #2	$98.90	8.287%	$107.0958	$107.10	$107.10	$107.10
Purchase #3	$199.56	11.654%	$222.8167	$222.82	$222.80	$222.80
Purchase #4	$61.93	12.464%	$69.649	$69.65	$69.65	$69.60
Purchase #5	$124.85	11.635%	$139.3763	$139.38	$139.40	$139.40
Purchase #6	$84.78	5.643%	$89.5641	$89.56	$89.55	$89.60
Purchase #7	$133.60	9.580%	$146.3989	$146.40	$146.40	$146.40
7 purchase totals =	$757.29		$833.2981	$833.31	$833.30	$833.30