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	$54.90	13.610%	$62.3719	$62.37	$62.35	$62.40
Purchase #2	$220.86	10.872%	$244.8719	$244.87	$244.85	$244.90
Purchase #3	$99.93	13.426%	$113.3466	$113.35	$113.35	$113.30
Purchase #4	$54.29	5.309%	$57.1723	$57.17	$57.15	$57.20
Purchase #5	$174.27	4.410%	$181.9553	$181.96	$181.95	$182.00
Purchase #6	$51.86	8.104%	$56.0627	$56.06	$56.05	$56.10
Purchase #7	$52.47	8.455%	$56.9063	$56.91	$56.90	$56.90
7 purchase totals =	$708.58		$772.6870	$772.69	$772.60	$772.80