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	$125.25	9.836%	$137.5696	$137.57	$137.55	$137.60
Purchase #2	$34.59	12.332%	$38.8556	$38.86	$38.85	$38.90
Purchase #3	$52.77	4.557%	$55.1747	$55.17	$55.15	$55.20
Purchase #4	$47.85	6.657%	$51.0354	$51.04	$51.05	$51.00
Purchase #5	$55.83	6.605%	$59.5176	$59.52	$59.50	$59.50
Purchase #6	$179.46	11.353%	$199.8341	$199.83	$199.85	$199.80
Purchase #7	$85.51	11.428%	$95.2821	$95.28	$95.30	$95.30
7 purchase totals =	$581.26		$637.2691	$637.27	$637.25	$637.30