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	$16.85	13.679%	$19.1549	$19.15	$19.15	$19.20
Purchase #2	$122.25	4.498%	$127.7488	$127.75	$127.75	$127.70
Purchase #3	$90.52	8.546%	$98.2558	$98.26	$98.25	$98.30
Purchase #4	$189.85	3.285%	$196.0866	$196.09	$196.10	$196.10
Purchase #5	$18.95	11.427%	$21.1154	$21.12	$21.10	$21.10
Purchase #6	$100.61	3.391%	$104.0217	$104.02	$104.00	$104.00
Purchase #7	$26.69	11.176%	$29.6729	$29.67	$29.65	$29.70
7 purchase totals =	$565.72		$596.0561	$596.06	$596.00	$596.10