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	$35.52	13.694%	$40.3841	$40.38	$40.40	$40.40
Purchase #2	$122.77	11.815%	$137.2753	$137.28	$137.30	$137.30
Purchase #3	$116.54	9.164%	$127.2197	$127.22	$127.20	$127.20
Purchase #4	$174.48	13.521%	$198.0714	$198.07	$198.05	$198.10
Purchase #5	$141.99	5.483%	$149.7753	$149.78	$149.80	$149.80
Purchase #6	$129.37	8.339%	$140.1582	$140.16	$140.15	$140.20
Purchase #7	$221.85	7.404%	$238.2758	$238.28	$238.30	$238.30
7 purchase totals =	$942.52		$1,031.1598	$1,031.17	$1,031.20	$1,031.30