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	$165.46	6.508%	$176.2281	$176.23	$176.25	$176.20
Purchase #2	$199.27	11.609%	$222.4033	$222.40	$222.40	$222.40
Purchase #3	$71.89	13.508%	$81.6009	$81.60	$81.60	$81.60
Purchase #4	$32.99	13.583%	$37.471	$37.47	$37.45	$37.50
Purchase #5	$111.50	9.442%	$122.0278	$122.03	$122.05	$122.00
Purchase #6	$105.80	6.685%	$112.8727	$112.87	$112.85	$112.90
Purchase #7	$125.74	10.768%	$139.2797	$139.28	$139.30	$139.30
7 purchase totals =	$812.65		$891.8835	$891.88	$891.90	$891.90