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	$178.25	6.346%	$189.5617	$189.56	$189.55	$189.60
Purchase #2	$99.36	6.761%	$106.0777	$106.08	$106.10	$106.10
Purchase #3	$51.67	11.146%	$57.4291	$57.43	$57.45	$57.40
Purchase #4	$109.98	12.397%	$123.6142	$123.61	$123.60	$123.60
Purchase #5	$12.69	6.713%	$13.5419	$13.54	$13.55	$13.50
Purchase #6	$66.99	8.544%	$72.7136	$72.71	$72.70	$72.70
Purchase #7	$57.92	3.486%	$59.9391	$59.94	$59.95	$59.90
7 purchase totals =	$576.86		$622.8773	$622.87	$622.90	$622.80