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	$229.83	13.416%	$260.664	$260.66	$260.65	$260.70
Purchase #2	$100.79	4.588%	$105.4142	$105.41	$105.40	$105.40
Purchase #3	$206.40	6.390%	$219.589	$219.59	$219.60	$219.60
Purchase #4	$21.26	5.190%	$22.3634	$22.36	$22.35	$22.40
Purchase #5	$118.47	7.337%	$127.1621	$127.16	$127.15	$127.20
Purchase #6	$35.78	5.248%	$37.6577	$37.66	$37.65	$37.70
Purchase #7	$184.25	13.113%	$208.4107	$208.41	$208.40	$208.40
7 purchase totals =	$896.78		$981.2611	$981.25	$981.20	$981.40