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	$130.30	10.735%	$144.2877	$144.29	$144.30	$144.30
Purchase #2	$166.25	12.644%	$187.2707	$187.27	$187.25	$187.30
Purchase #3	$239.61	13.253%	$271.3655	$271.37	$271.35	$271.40
Purchase #4	$135.80	12.636%	$152.9597	$152.96	$152.95	$153.00
Purchase #5	$39.48	9.771%	$43.3376	$43.34	$43.35	$43.30
Purchase #6	$116.98	8.675%	$127.128	$127.13	$127.15	$127.10
Purchase #7	$87.98	7.868%	$94.9023	$94.90	$94.90	$94.90
7 purchase totals =	$916.40		$1,021.2515	$1,021.26	$1,021.25	$1,021.30