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	$113.39	12.277%	$127.3109	$127.31	$127.30	$127.30
Purchase #2	$39.28	5.703%	$41.5201	$41.52	$41.50	$41.50
Purchase #3	$154.47	7.619%	$166.2391	$166.24	$166.25	$166.20
Purchase #4	$95.61	5.549%	$100.9154	$100.92	$100.90	$100.90
Purchase #5	$117.58	9.790%	$129.0911	$129.09	$129.10	$129.10
Purchase #6	$10.64	10.810%	$11.7902	$11.79	$11.80	$11.80
Purchase #7	$18.58	3.234%	$19.1809	$19.18	$19.20	$19.20
7 purchase totals =	$549.55		$596.0477	$596.05	$596.05	$596.00