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	$207.37	7.267%	$222.4396	$222.44	$222.45	$222.40
Purchase #2	$146.68	5.610%	$154.9087	$154.91	$154.90	$154.90
Purchase #3	$242.96	12.128%	$272.4262	$272.43	$272.45	$272.40
Purchase #4	$53.53	11.302%	$59.58	$59.58	$59.60	$59.60
Purchase #5	$250.78	4.596%	$262.3058	$262.31	$262.30	$262.30
Purchase #6	$238.56	8.303%	$258.3676	$258.37	$258.35	$258.40
Purchase #7	$56.43	12.206%	$63.3178	$63.32	$63.30	$63.30
7 purchase totals =	$1,196.31		$1,293.3457	$1,293.36	$1,293.35	$1,293.30