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	$36.76	7.396%	$39.4788	$39.48	$39.50	$39.50
Purchase #2	$50.72	5.434%	$53.4761	$53.48	$53.50	$53.50
Purchase #3	$81.77	12.566%	$92.0452	$92.05	$92.05	$92.00
Purchase #4	$186.69	3.668%	$193.5378	$193.54	$193.55	$193.50
Purchase #5	$12.54	10.208%	$13.8201	$13.82	$13.80	$13.80
Purchase #6	$31.83	11.185%	$35.3902	$35.39	$35.40	$35.40
Purchase #7	$29.94	8.576%	$32.5077	$32.51	$32.50	$32.50
7 purchase totals =	$430.25		$460.2559	$460.27	$460.30	$460.20