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	$98.95	12.807%	$111.6225	$111.62	$111.60	$111.60
Purchase #2	$73.99	13.452%	$83.9431	$83.94	$83.95	$83.90
Purchase #3	$11.92	4.555%	$12.463	$12.46	$12.45	$12.50
Purchase #4	$101.52	4.655%	$106.2458	$106.25	$106.25	$106.20
Purchase #5	$153.95	7.154%	$164.9636	$164.96	$164.95	$165.00
Purchase #6	$97.39	12.635%	$109.6952	$109.70	$109.70	$109.70
Purchase #7	$82.45	12.389%	$92.6647	$92.66	$92.65	$92.70
7 purchase totals =	$620.17		$681.5979	$681.59	$681.55	$681.60