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	$128.60	11.425%	$143.2926	$143.29	$143.30	$143.30
Purchase #2	$172.34	12.179%	$193.3293	$193.33	$193.35	$193.30
Purchase #3	$166.85	3.474%	$172.6464	$172.65	$172.65	$172.60
Purchase #4	$56.69	3.768%	$58.8261	$58.83	$58.85	$58.80
Purchase #5	$10.67	13.276%	$12.0865	$12.09	$12.10	$12.10
Purchase #6	$82.97	8.834%	$90.2996	$90.30	$90.30	$90.30
Purchase #7	$70.95	13.583%	$80.5871	$80.59	$80.60	$80.60
7 purchase totals =	$689.07		$751.0676	$751.08	$751.15	$751.00