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	$38.79	12.350%	$43.5806	$43.58	$43.60	$43.60
Purchase #2	$56.69	13.141%	$64.1396	$64.14	$64.15	$64.10
Purchase #3	$124.92	11.495%	$139.2796	$139.28	$139.30	$139.30
Purchase #4	$165.49	6.526%	$176.2899	$176.29	$176.30	$176.30
Purchase #5	$208.32	6.367%	$221.5837	$221.58	$221.60	$221.60
Purchase #6	$96.48	3.866%	$100.2099	$100.21	$100.20	$100.20
Purchase #7	$181.74	9.572%	$199.1362	$199.14	$199.15	$199.10
7 purchase totals =	$872.43		$944.2195	$944.22	$944.30	$944.20