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	$31.54	11.396%	$35.1343	$35.13	$35.15	$35.10
Purchase #2	$39.90	7.851%	$43.0325	$43.03	$43.05	$43.00
Purchase #3	$11.44	9.466%	$12.5229	$12.52	$12.50	$12.50
Purchase #4	$126.60	7.567%	$136.1798	$136.18	$136.20	$136.20
Purchase #5	$85.54	5.594%	$90.3251	$90.33	$90.35	$90.30
Purchase #6	$70.84	5.684%	$74.8665	$74.87	$74.85	$74.90
Purchase #7	$72.27	5.345%	$76.1328	$76.13	$76.15	$76.10
7 purchase totals =	$438.13		$468.1939	$468.19	$468.25	$468.10