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	$11.62	4.514%	$12.1445	$12.14	$12.15	$12.10
Purchase #2	$173.75	5.628%	$183.5287	$183.53	$183.55	$183.50
Purchase #3	$40.27	6.721%	$42.9765	$42.98	$43.00	$43.00
Purchase #4	$110.72	12.530%	$124.5932	$124.59	$124.60	$124.60
Purchase #5	$121.25	13.737%	$137.9061	$137.91	$137.90	$137.90
Purchase #6	$44.80	7.393%	$48.1121	$48.11	$48.10	$48.10
Purchase #7	$90.44	11.581%	$100.9139	$100.91	$100.90	$100.90
7 purchase totals =	$592.85		$650.1750	$650.17	$650.20	$650.10