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	$105.30	12.815%	$118.7942	$118.79	$118.80	$118.80
Purchase #2	$117.98	7.530%	$126.8639	$126.86	$126.85	$126.90
Purchase #3	$170.39	8.227%	$184.408	$184.41	$184.40	$184.40
Purchase #4	$129.75	3.762%	$134.6312	$134.63	$134.65	$134.60
Purchase #5	$80.93	10.769%	$89.6454	$89.65	$89.65	$89.60
Purchase #6	$56.86	8.354%	$61.6101	$61.61	$61.60	$61.60
Purchase #7	$36.33	4.736%	$38.0506	$38.05	$38.05	$38.10
7 purchase totals =	$697.54		$754.0034	$754.00	$754.00	$754.00