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	$249.95	10.358%	$275.8398	$275.84	$275.85	$275.80
Purchase #2	$13.86	10.495%	$15.3146	$15.31	$15.30	$15.30
Purchase #3	$184.84	10.379%	$204.0245	$204.02	$204.00	$204.00
Purchase #4	$53.84	13.566%	$61.1439	$61.14	$61.15	$61.10
Purchase #5	$97.48	11.172%	$108.3705	$108.37	$108.35	$108.40
Purchase #6	$40.72	11.223%	$45.29	$45.29	$45.30	$45.30
Purchase #7	$43.36	3.530%	$44.8906	$44.89	$44.90	$44.90
7 purchase totals =	$684.05		$754.8739	$754.86	$754.85	$754.80