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	$221.49	6.109%	$235.0208	$235.02	$235.00	$235.00
Purchase #2	$159.78	5.217%	$168.1157	$168.12	$168.10	$168.10
Purchase #3	$78.37	11.757%	$87.584	$87.58	$87.60	$87.60
Purchase #4	$99.90	13.302%	$113.1887	$113.19	$113.20	$113.20
Purchase #5	$99.60	11.509%	$111.063	$111.06	$111.05	$111.10
Purchase #6	$43.53	5.543%	$45.9429	$45.94	$45.95	$45.90
Purchase #7	$116.27	3.152%	$119.9348	$119.93	$119.95	$119.90
7 purchase totals =	$818.94		$880.8499	$880.84	$880.85	$880.80