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	$44.83	12.131%	$50.2683	$50.27	$50.25	$50.30
Purchase #2	$164.49	13.797%	$187.1847	$187.18	$187.20	$187.20
Purchase #3	$137.69	7.505%	$148.0236	$148.02	$148.00	$148.00
Purchase #4	$62.52	8.633%	$67.9174	$67.92	$67.90	$67.90
Purchase #5	$109.34	9.363%	$119.5775	$119.58	$119.60	$119.60
Purchase #6	$211.28	5.139%	$222.1377	$222.14	$222.15	$222.10
Purchase #7	$99.56	6.245%	$105.7775	$105.78	$105.80	$105.80
7 purchase totals =	$829.71		$900.8867	$900.89	$900.90	$900.90