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	$242.34	12.430%	$272.4629	$272.46	$272.45	$272.50
Purchase #2	$173.61	8.213%	$187.8686	$187.87	$187.85	$187.90
Purchase #3	$39.56	8.253%	$42.8249	$42.82	$42.80	$42.80
Purchase #4	$192.42	7.548%	$206.9439	$206.94	$206.95	$206.90
Purchase #5	$147.28	11.776%	$164.6237	$164.62	$164.60	$164.60
Purchase #6	$56.95	10.323%	$62.8289	$62.83	$62.85	$62.80
Purchase #7	$66.47	11.468%	$74.0928	$74.09	$74.10	$74.10
7 purchase totals =	$918.63		$1,011.6457	$1,011.63	$1,011.60	$1,011.60