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	$27.75	12.694%	$31.2726	$31.27	$31.25	$31.30
Purchase #2	$42.97	5.153%	$45.1842	$45.18	$45.20	$45.20
Purchase #3	$73.39	8.866%	$79.8968	$79.90	$79.90	$79.90
Purchase #4	$116.71	9.369%	$127.6446	$127.64	$127.65	$127.60
Purchase #5	$17.50	13.819%	$19.9183	$19.92	$19.90	$19.90
Purchase #6	$139.83	8.173%	$151.2583	$151.26	$151.25	$151.30
Purchase #7	$51.70	10.715%	$57.2397	$57.24	$57.25	$57.20
7 purchase totals =	$469.85		$512.4145	$512.41	$512.40	$512.40