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	$245.32	13.862%	$279.3263	$279.33	$279.35	$279.30
Purchase #2	$238.40	7.225%	$255.6244	$255.62	$255.60	$255.60
Purchase #3	$115.68	12.759%	$130.4396	$130.44	$130.45	$130.40
Purchase #4	$214.69	11.193%	$238.7203	$238.72	$238.70	$238.70
Purchase #5	$208.62	6.551%	$222.2867	$222.29	$222.30	$222.30
Purchase #6	$68.60	3.655%	$71.1073	$71.11	$71.10	$71.10
Purchase #7	$51.37	8.418%	$55.6943	$55.69	$55.70	$55.70
7 purchase totals =	$1,142.68		$1,253.1989	$1,253.20	$1,253.20	$1,253.10