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	$99.30	10.278%	$109.5061	$109.51	$109.50	$109.50
Purchase #2	$31.50	10.443%	$34.7895	$34.79	$34.80	$34.80
Purchase #3	$120.92	8.720%	$131.4642	$131.46	$131.45	$131.50
Purchase #4	$244.54	13.103%	$276.5821	$276.58	$276.60	$276.60
Purchase #5	$223.83	11.625%	$249.8502	$249.85	$249.85	$249.90
Purchase #6	$220.32	13.783%	$250.6867	$250.69	$250.70	$250.70
Purchase #7	$208.67	10.327%	$230.2194	$230.22	$230.20	$230.20
7 purchase totals =	$1,149.08		$1,283.0982	$1,283.10	$1,283.10	$1,283.20