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	$120.45	13.163%	$136.3048	$136.30	$136.30	$136.30
Purchase #2	$28.71	12.743%	$32.3685	$32.37	$32.35	$32.40
Purchase #3	$173.59	7.834%	$187.189	$187.19	$187.20	$187.20
Purchase #4	$42.97	12.777%	$48.4603	$48.46	$48.45	$48.50
Purchase #5	$158.38	12.634%	$178.3897	$178.39	$178.40	$178.40
Purchase #6	$85.37	6.428%	$90.8576	$90.86	$90.85	$90.90
Purchase #7	$122.68	3.721%	$127.2449	$127.24	$127.25	$127.20
7 purchase totals =	$732.15		$800.8148	$800.81	$800.80	$800.90