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	$166.66	13.109%	$188.5075	$188.51	$188.50	$188.50
Purchase #2	$241.36	9.714%	$264.8057	$264.81	$264.80	$264.80
Purchase #3	$39.58	10.782%	$43.8475	$43.85	$43.85	$43.80
Purchase #4	$83.60	8.272%	$90.5154	$90.52	$90.50	$90.50
Purchase #5	$49.77	8.324%	$53.9129	$53.91	$53.90	$53.90
Purchase #6	$235.25	5.830%	$248.9651	$248.97	$248.95	$249.00
Purchase #7	$15.78	10.852%	$17.4924	$17.49	$17.50	$17.50
7 purchase totals =	$832.00		$908.0465	$908.06	$908.00	$908.00