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	$156.39	13.649%	$177.7357	$177.74	$177.75	$177.70
Purchase #2	$74.78	5.201%	$78.6693	$78.67	$78.65	$78.70
Purchase #3	$111.60	13.280%	$126.4205	$126.42	$126.40	$126.40
Purchase #4	$78.82	4.410%	$82.296	$82.30	$82.30	$82.30
Purchase #5	$32.55	5.465%	$34.3289	$34.33	$34.35	$34.30
Purchase #6	$250.45	12.868%	$282.6779	$282.68	$282.70	$282.70
Purchase #7	$49.33	5.409%	$51.9983	$52.00	$52.00	$52.00
7 purchase totals =	$753.92		$834.1266	$834.14	$834.15	$834.10