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	$123.79	10.241%	$136.4673	$136.47	$136.45	$136.50
Purchase #2	$244.67	4.600%	$255.9248	$255.92	$255.90	$255.90
Purchase #3	$140.65	13.471%	$159.597	$159.60	$159.60	$159.60
Purchase #4	$47.60	4.555%	$49.7682	$49.77	$49.75	$49.80
Purchase #5	$205.65	5.353%	$216.6584	$216.66	$216.65	$216.70
Purchase #6	$161.94	8.760%	$176.1259	$176.13	$176.15	$176.10
Purchase #7	$69.82	12.502%	$78.5489	$78.55	$78.55	$78.50
7 purchase totals =	$994.12		$1,073.0905	$1,073.10	$1,073.05	$1,073.10