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	$220.74	12.523%	$248.3833	$248.38	$248.40	$248.40
Purchase #2	$56.75	4.723%	$59.4303	$59.43	$59.45	$59.40
Purchase #3	$11.78	4.676%	$12.3308	$12.33	$12.35	$12.30
Purchase #4	$7.64	11.193%	$8.4951	$8.50	$8.50	$8.50
Purchase #5	$103.64	10.281%	$114.2952	$114.30	$114.30	$114.30
Purchase #6	$34.75	7.784%	$37.4549	$37.45	$37.45	$37.50
Purchase #7	$233.96	6.597%	$249.3943	$249.39	$249.40	$249.40
7 purchase totals =	$669.26		$729.7839	$729.78	$729.85	$729.80