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	$230.77	11.447%	$257.1862	$257.19	$257.20	$257.20
Purchase #2	$121.27	9.163%	$132.382	$132.38	$132.40	$132.40
Purchase #3	$35.27	13.837%	$40.1503	$40.15	$40.15	$40.20
Purchase #4	$10.43	3.785%	$10.8248	$10.82	$10.80	$10.80
Purchase #5	$249.36	10.396%	$275.2835	$275.28	$275.30	$275.30
Purchase #6	$66.47	7.489%	$71.4479	$71.45	$71.45	$71.40
Purchase #7	$6.90	3.641%	$7.1512	$7.15	$7.15	$7.20
7 purchase totals =	$720.47		$794.4259	$794.42	$794.45	$794.50