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	$172.67	3.868%	$179.3489	$179.35	$179.35	$179.30
Purchase #2	$138.38	8.617%	$150.3042	$150.30	$150.30	$150.30
Purchase #3	$54.27	10.407%	$59.9179	$59.92	$59.90	$59.90
Purchase #4	$93.50	6.532%	$99.6074	$99.61	$99.60	$99.60
Purchase #5	$234.98	9.664%	$257.6885	$257.69	$257.70	$257.70
Purchase #6	$44.69	11.683%	$49.9111	$49.91	$49.90	$49.90
Purchase #7	$102.39	3.174%	$105.6399	$105.64	$105.65	$105.60
7 purchase totals =	$840.88		$902.4179	$902.42	$902.40	$902.30