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	$165.91	13.855%	$188.8968	$188.90	$188.90	$188.90
Purchase #2	$222.51	9.147%	$242.863	$242.86	$242.85	$242.90
Purchase #3	$94.39	7.508%	$101.4768	$101.48	$101.50	$101.50
Purchase #4	$207.26	10.470%	$228.9601	$228.96	$228.95	$229.00
Purchase #5	$49.52	10.718%	$54.8276	$54.83	$54.85	$54.80
Purchase #6	$51.94	4.715%	$54.389	$54.39	$54.40	$54.40
Purchase #7	$99.62	5.668%	$105.2665	$105.27	$105.25	$105.30
7 purchase totals =	$891.15		$976.6798	$976.69	$976.70	$976.80