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	$79.65	13.370%	$90.2992	$90.30	$90.30	$90.30
Purchase #2	$14.54	9.571%	$15.9316	$15.93	$15.95	$15.90
Purchase #3	$49.53	7.649%	$53.3185	$53.32	$53.30	$53.30
Purchase #4	$157.95	5.197%	$166.1587	$166.16	$166.15	$166.20
Purchase #5	$25.56	11.362%	$28.4641	$28.46	$28.45	$28.50
Purchase #6	$127.83	13.447%	$145.0193	$145.02	$145.00	$145.00
Purchase #7	$220.32	7.645%	$237.1635	$237.16	$237.15	$237.20
7 purchase totals =	$675.38		$736.3549	$736.35	$736.30	$736.40