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	$178.40	5.548%	$188.2976	$188.30	$188.30	$188.30
Purchase #2	$234.90	9.760%	$257.8262	$257.83	$257.85	$257.80
Purchase #3	$12.29	6.626%	$13.1043	$13.10	$13.10	$13.10
Purchase #4	$155.76	5.501%	$164.3284	$164.33	$164.35	$164.30
Purchase #5	$113.46	4.223%	$118.2514	$118.25	$118.25	$118.30
Purchase #6	$18.38	4.126%	$19.1384	$19.14	$19.15	$19.10
Purchase #7	$5.27	4.336%	$5.4985	$5.50	$5.50	$5.50
7 purchase totals =	$718.46		$766.4448	$766.45	$766.50	$766.40