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	$83.73	5.743%	$88.5386	$88.54	$88.55	$88.50
Purchase #2	$52.96	5.432%	$55.8368	$55.84	$55.85	$55.80
Purchase #3	$153.57	5.852%	$162.5569	$162.56	$162.55	$162.60
Purchase #4	$172.55	3.208%	$178.0854	$178.09	$178.10	$178.10
Purchase #5	$34.26	9.404%	$37.4818	$37.48	$37.50	$37.50
Purchase #6	$33.60	12.156%	$37.6844	$37.68	$37.70	$37.70
Purchase #7	$230.95	3.336%	$238.6545	$238.65	$238.65	$238.70
7 purchase totals =	$761.62		$798.8384	$798.84	$798.90	$798.90