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	$56.85	13.414%	$64.4759	$64.48	$64.50	$64.50
Purchase #2	$240.91	8.137%	$260.5128	$260.51	$260.50	$260.50
Purchase #3	$250.30	3.631%	$259.3884	$259.39	$259.40	$259.40
Purchase #4	$159.89	11.566%	$178.3829	$178.38	$178.40	$178.40
Purchase #5	$235.47	7.822%	$253.8885	$253.89	$253.90	$253.90
Purchase #6	$33.77	13.739%	$38.4097	$38.41	$38.40	$38.40
Purchase #7	$117.95	12.293%	$132.4496	$132.45	$132.45	$132.40
7 purchase totals =	$1,095.14		$1,187.5078	$1,187.51	$1,187.55	$1,187.50