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	$31.29	9.561%	$34.2816	$34.28	$34.30	$34.30
Purchase #2	$125.43	13.309%	$142.1235	$142.12	$142.10	$142.10
Purchase #3	$153.28	10.604%	$169.5338	$169.53	$169.55	$169.50
Purchase #4	$122.60	7.192%	$131.4174	$131.42	$131.40	$131.40
Purchase #5	$148.43	6.476%	$158.0423	$158.04	$158.05	$158.00
Purchase #6	$132.75	7.302%	$142.4434	$142.44	$142.45	$142.40
Purchase #7	$13.83	4.482%	$14.4499	$14.45	$14.45	$14.40
7 purchase totals =	$727.61		$792.2919	$792.28	$792.30	$792.10