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	$26.84	9.833%	$29.4792	$29.48	$29.50	$29.50
Purchase #2	$50.34	12.598%	$56.6818	$56.68	$56.70	$56.70
Purchase #3	$92.29	12.511%	$103.8364	$103.84	$103.85	$103.80
Purchase #4	$54.56	8.666%	$59.2882	$59.29	$59.30	$59.30
Purchase #5	$98.37	4.784%	$103.076	$103.08	$103.10	$103.10
Purchase #6	$81.47	8.543%	$88.43	$88.43	$88.45	$88.40
Purchase #7	$148.65	8.201%	$160.8408	$160.84	$160.85	$160.80
7 purchase totals =	$552.52		$601.6324	$601.64	$601.75	$601.60