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	$60.74	9.655%	$66.6044	$66.60	$66.60	$66.60
Purchase #2	$21.93	12.363%	$24.6412	$24.64	$24.65	$24.60
Purchase #3	$244.29	9.405%	$267.2655	$267.27	$267.25	$267.30
Purchase #4	$39.81	7.586%	$42.83	$42.83	$42.85	$42.80
Purchase #5	$223.34	11.311%	$248.602	$248.60	$248.60	$248.60
Purchase #6	$142.68	9.277%	$155.9164	$155.92	$155.90	$155.90
Purchase #7	$238.32	13.834%	$271.2892	$271.29	$271.30	$271.30
7 purchase totals =	$971.11		$1,077.1487	$1,077.15	$1,077.15	$1,077.10