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	$81.29	10.425%	$89.7645	$89.76	$89.75	$89.80
Purchase #2	$217.46	11.245%	$241.9134	$241.91	$241.90	$241.90
Purchase #3	$50.75	11.443%	$56.5573	$56.56	$56.55	$56.60
Purchase #4	$116.43	9.588%	$127.5933	$127.59	$127.60	$127.60
Purchase #5	$197.25	13.530%	$223.9379	$223.94	$223.95	$223.90
Purchase #6	$41.31	5.597%	$43.6221	$43.62	$43.60	$43.60
Purchase #7	$25.83	12.739%	$29.1205	$29.12	$29.10	$29.10
7 purchase totals =	$730.32		$812.5090	$812.50	$812.45	$812.50