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	$80.31	11.697%	$89.7039	$89.70	$89.70	$89.70
Purchase #2	$192.39	12.867%	$217.1448	$217.14	$217.15	$217.10
Purchase #3	$160.98	12.342%	$180.8482	$180.85	$180.85	$180.80
Purchase #4	$51.97	3.220%	$53.6434	$53.64	$53.65	$53.60
Purchase #5	$246.79	5.818%	$261.1482	$261.15	$261.15	$261.10
Purchase #6	$78.53	8.240%	$85.0009	$85.00	$85.00	$85.00
Purchase #7	$118.38	12.862%	$133.606	$133.61	$133.60	$133.60
7 purchase totals =	$929.35		$1,021.0954	$1,021.09	$1,021.10	$1,020.90