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	$127.43	7.334%	$136.7757	$136.78	$136.80	$136.80
Purchase #2	$130.52	4.840%	$136.8372	$136.84	$136.85	$136.80
Purchase #3	$104.48	6.308%	$111.0706	$111.07	$111.05	$111.10
Purchase #4	$19.74	7.606%	$21.2414	$21.24	$21.25	$21.20
Purchase #5	$92.59	9.297%	$101.1981	$101.20	$101.20	$101.20
Purchase #6	$57.75	12.262%	$64.8313	$64.83	$64.85	$64.80
Purchase #7	$84.84	8.238%	$91.8291	$91.83	$91.85	$91.80
7 purchase totals =	$617.35		$663.7834	$663.79	$663.85	$663.70