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	$90.76	11.188%	$100.9142	$100.91	$100.90	$100.90
Purchase #2	$152.64	9.483%	$167.1149	$167.11	$167.10	$167.10
Purchase #3	$211.68	8.873%	$230.4624	$230.46	$230.45	$230.50
Purchase #4	$32.25	6.240%	$34.2624	$34.26	$34.25	$34.30
Purchase #5	$56.70	9.479%	$62.0746	$62.07	$62.05	$62.10
Purchase #6	$182.45	4.346%	$190.3793	$190.38	$190.40	$190.40
Purchase #7	$91.68	3.573%	$94.9557	$94.96	$94.95	$95.00
7 purchase totals =	$818.16		$880.1635	$880.15	$880.10	$880.30