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	$165.72	8.460%	$179.7399	$179.74	$179.75	$179.70
Purchase #2	$136.35	3.189%	$140.6982	$140.70	$140.70	$140.70
Purchase #3	$78.85	12.231%	$88.4941	$88.49	$88.50	$88.50
Purchase #4	$52.89	13.665%	$60.1174	$60.12	$60.10	$60.10
Purchase #5	$49.75	9.780%	$54.6156	$54.62	$54.60	$54.60
Purchase #6	$37.82	6.701%	$40.3543	$40.35	$40.35	$40.40
Purchase #7	$221.94	5.395%	$233.9137	$233.91	$233.90	$233.90
7 purchase totals =	$743.32		$797.9332	$797.93	$797.90	$797.90