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	$159.50	12.178%	$178.9239	$178.92	$178.90	$178.90
Purchase #2	$34.40	9.436%	$37.646	$37.65	$37.65	$37.60
Purchase #3	$187.50	11.253%	$208.5994	$208.60	$208.60	$208.60
Purchase #4	$67.29	5.113%	$70.7305	$70.73	$70.75	$70.70
Purchase #5	$108.90	7.306%	$116.8562	$116.86	$116.85	$116.90
Purchase #6	$139.89	6.696%	$149.257	$149.26	$149.25	$149.30
Purchase #7	$203.42	6.216%	$216.0646	$216.06	$216.05	$216.10
7 purchase totals =	$900.90		$978.0776	$978.08	$978.05	$978.10