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	$20.41	10.343%	$22.521	$22.52	$22.50	$22.50
Purchase #2	$123.86	11.140%	$137.658	$137.66	$137.65	$137.70
Purchase #3	$39.99	8.377%	$43.34	$43.34	$43.35	$43.30
Purchase #4	$105.39	5.674%	$111.3698	$111.37	$111.35	$111.40
Purchase #5	$154.79	3.316%	$159.9228	$159.92	$159.90	$159.90
Purchase #6	$21.36	12.280%	$23.983	$23.98	$24.00	$24.00
Purchase #7	$55.81	3.753%	$57.9045	$57.90	$57.90	$57.90
7 purchase totals =	$521.61		$556.6991	$556.69	$556.65	$556.70