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	$48.36	9.850%	$53.1235	$53.12	$53.10	$53.10
Purchase #2	$55.51	10.146%	$61.142	$61.14	$61.15	$61.10
Purchase #3	$113.60	4.320%	$118.5075	$118.51	$118.50	$118.50
Purchase #4	$41.49	10.685%	$45.9232	$45.92	$45.90	$45.90
Purchase #5	$149.27	8.381%	$161.7803	$161.78	$161.80	$161.80
Purchase #6	$32.78	4.255%	$34.1748	$34.17	$34.15	$34.20
Purchase #7	$110.52	4.571%	$115.5719	$115.57	$115.55	$115.60
7 purchase totals =	$551.53		$590.2232	$590.21	$590.15	$590.20