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	$149.25	4.706%	$156.2737	$156.27	$156.25	$156.30
Purchase #2	$203.80	8.329%	$220.7745	$220.77	$220.75	$220.80
Purchase #3	$207.57	5.323%	$218.619	$218.62	$218.60	$218.60
Purchase #4	$39.91	6.300%	$42.4243	$42.42	$42.40	$42.40
Purchase #5	$33.64	5.454%	$35.4747	$35.47	$35.45	$35.50
Purchase #6	$71.38	12.604%	$80.3767	$80.38	$80.40	$80.40
Purchase #7	$211.90	13.872%	$241.2948	$241.29	$241.30	$241.30
7 purchase totals =	$917.45		$995.2377	$995.22	$995.15	$995.30