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	$146.50	13.666%	$166.5207	$166.52	$166.50	$166.50
Purchase #2	$47.84	13.635%	$54.363	$54.36	$54.35	$54.40
Purchase #3	$150.53	3.581%	$155.9205	$155.92	$155.90	$155.90
Purchase #4	$58.49	12.298%	$65.6831	$65.68	$65.70	$65.70
Purchase #5	$44.95	8.171%	$48.6229	$48.62	$48.60	$48.60
Purchase #6	$64.34	8.799%	$70.0013	$70.00	$70.00	$70.00
Purchase #7	$90.59	9.368%	$99.0765	$99.08	$99.10	$99.10
7 purchase totals =	$603.24		$660.1880	$660.18	$660.15	$660.20