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	$122.43	6.592%	$130.5006	$130.50	$130.50	$130.50
Purchase #2	$179.56	5.353%	$189.1718	$189.17	$189.15	$189.20
Purchase #3	$40.88	4.185%	$42.5908	$42.59	$42.60	$42.60
Purchase #4	$18.61	13.477%	$21.1181	$21.12	$21.10	$21.10
Purchase #5	$121.39	12.425%	$136.4727	$136.47	$136.45	$136.50
Purchase #6	$132.28	7.118%	$141.6957	$141.70	$141.70	$141.70
Purchase #7	$91.43	9.238%	$99.8763	$99.88	$99.90	$99.90
7 purchase totals =	$706.58		$761.4260	$761.43	$761.40	$761.50