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	$33.90	4.176%	$35.3157	$35.32	$35.30	$35.30
Purchase #2	$114.80	10.811%	$127.211	$127.21	$127.20	$127.20
Purchase #3	$26.40	11.589%	$29.4595	$29.46	$29.45	$29.50
Purchase #4	$104.56	13.539%	$118.7164	$118.72	$118.70	$118.70
Purchase #5	$33.90	3.745%	$35.1696	$35.17	$35.15	$35.20
Purchase #6	$198.88	10.250%	$219.2652	$219.27	$219.25	$219.30
Purchase #7	$225.59	9.462%	$246.9353	$246.94	$246.95	$246.90
7 purchase totals =	$738.03		$812.0727	$812.09	$812.00	$812.10