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	$235.28	3.374%	$243.2183	$243.22	$243.20	$243.20
Purchase #2	$99.31	11.861%	$111.0892	$111.09	$111.10	$111.10
Purchase #3	$105.43	11.349%	$117.3953	$117.40	$117.40	$117.40
Purchase #4	$246.43	13.297%	$279.1978	$279.20	$279.20	$279.20
Purchase #5	$91.64	13.787%	$104.2744	$104.27	$104.25	$104.30
Purchase #6	$135.86	4.239%	$141.6191	$141.62	$141.60	$141.60
Purchase #7	$138.83	4.646%	$145.28	$145.28	$145.30	$145.30
7 purchase totals =	$1,052.78		$1,142.0741	$1,142.08	$1,142.05	$1,142.10