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	$77.32	7.641%	$83.228	$83.23	$83.25	$83.20
Purchase #2	$228.98	6.562%	$244.0057	$244.01	$244.00	$244.00
Purchase #3	$41.80	3.264%	$43.1644	$43.16	$43.15	$43.20
Purchase #4	$34.25	13.379%	$38.8323	$38.83	$38.85	$38.80
Purchase #5	$54.97	3.598%	$56.9478	$56.95	$56.95	$56.90
Purchase #6	$66.93	6.288%	$71.1386	$71.14	$71.15	$71.10
Purchase #7	$122.34	6.497%	$130.2884	$130.29	$130.30	$130.30
7 purchase totals =	$626.59		$667.6052	$667.61	$667.65	$667.50