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	$69.34	13.252%	$78.5289	$78.53	$78.55	$78.50
Purchase #2	$44.70	3.818%	$46.4066	$46.41	$46.40	$46.40
Purchase #3	$107.55	5.536%	$113.504	$113.50	$113.50	$113.50
Purchase #4	$173.89	11.798%	$194.4055	$194.41	$194.40	$194.40
Purchase #5	$172.64	9.748%	$189.4689	$189.47	$189.45	$189.50
Purchase #6	$9.31	13.741%	$10.5893	$10.59	$10.60	$10.60
Purchase #7	$86.88	13.631%	$98.7226	$98.72	$98.70	$98.70
7 purchase totals =	$664.31		$731.6258	$731.63	$731.60	$731.60