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	$16.34	13.196%	$18.4962	$18.50	$18.50	$18.50
Purchase #2	$148.31	11.826%	$165.8491	$165.85	$165.85	$165.80
Purchase #3	$67.86	7.516%	$72.9604	$72.96	$72.95	$73.00
Purchase #4	$181.87	4.783%	$190.5688	$190.57	$190.55	$190.60
Purchase #5	$32.60	5.792%	$34.4882	$34.49	$34.50	$34.50
Purchase #6	$87.55	4.632%	$91.6053	$91.61	$91.60	$91.60
Purchase #7	$139.92	7.722%	$150.7246	$150.72	$150.70	$150.70
7 purchase totals =	$674.45		$724.6926	$724.70	$724.65	$724.70