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	$38.85	11.480%	$43.31	$43.31	$43.30	$43.30
Purchase #2	$108.70	8.513%	$117.9536	$117.95	$117.95	$118.00
Purchase #3	$203.68	13.166%	$230.4965	$230.50	$230.50	$230.50
Purchase #4	$118.43	4.501%	$123.7605	$123.76	$123.75	$123.80
Purchase #5	$216.75	3.115%	$223.5018	$223.50	$223.50	$223.50
Purchase #6	$72.97	7.494%	$78.4384	$78.44	$78.45	$78.40
Purchase #7	$50.63	10.577%	$55.9851	$55.99	$56.00	$56.00
7 purchase totals =	$810.01		$873.4459	$873.45	$873.45	$873.50