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	$18.66	10.604%	$20.6387	$20.64	$20.65	$20.60
Purchase #2	$165.91	10.132%	$182.72	$182.72	$182.70	$182.70
Purchase #3	$98.93	12.676%	$111.4704	$111.47	$111.45	$111.50
Purchase #4	$219.36	9.766%	$240.7827	$240.78	$240.80	$240.80
Purchase #5	$179.60	8.277%	$194.4655	$194.47	$194.45	$194.50
Purchase #6	$168.38	9.390%	$184.1909	$184.19	$184.20	$184.20
Purchase #7	$187.29	10.597%	$207.1371	$207.14	$207.15	$207.10
7 purchase totals =	$1,038.13		$1,141.4053	$1,141.41	$1,141.40	$1,141.40