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	$140.61	4.295%	$146.6492	$146.65	$146.65	$146.60
Purchase #2	$49.37	10.305%	$54.4576	$54.46	$54.45	$54.50
Purchase #3	$132.36	13.867%	$150.7144	$150.71	$150.70	$150.70
Purchase #4	$124.29	6.623%	$132.5217	$132.52	$132.50	$132.50
Purchase #5	$51.54	11.315%	$57.3718	$57.37	$57.35	$57.40
Purchase #6	$109.39	9.384%	$119.6552	$119.66	$119.65	$119.70
Purchase #7	$151.60	8.281%	$164.154	$164.15	$164.15	$164.20
7 purchase totals =	$759.16		$825.5239	$825.52	$825.45	$825.60