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	$57.41	10.181%	$63.2549	$63.25	$63.25	$63.30
Purchase #2	$57.97	6.626%	$61.8111	$61.81	$61.80	$61.80
Purchase #3	$235.88	7.649%	$253.9225	$253.92	$253.90	$253.90
Purchase #4	$82.60	9.809%	$90.7022	$90.70	$90.70	$90.70
Purchase #5	$240.85	5.332%	$253.6921	$253.69	$253.70	$253.70
Purchase #6	$135.82	9.387%	$148.5694	$148.57	$148.55	$148.60
Purchase #7	$24.94	13.602%	$28.3323	$28.33	$28.35	$28.30
7 purchase totals =	$835.47		$900.2845	$900.27	$900.25	$900.30