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	$14.31	5.443%	$15.0889	$15.09	$15.10	$15.10
Purchase #2	$32.78	8.438%	$35.546	$35.55	$35.55	$35.50
Purchase #3	$34.55	7.199%	$37.0373	$37.04	$37.05	$37.00
Purchase #4	$181.39	3.323%	$187.4176	$187.42	$187.40	$187.40
Purchase #5	$85.86	5.796%	$90.8364	$90.84	$90.85	$90.80
Purchase #6	$49.95	4.428%	$52.1618	$52.16	$52.15	$52.20
Purchase #7	$184.85	8.151%	$199.9171	$199.92	$199.90	$199.90
7 purchase totals =	$583.69		$618.0051	$618.02	$618.00	$617.90