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	$158.31	13.160%	$179.1436	$179.14	$179.15	$179.10
Purchase #2	$24.91	9.340%	$27.2366	$27.24	$27.25	$27.20
Purchase #3	$179.41	10.802%	$198.7899	$198.79	$198.80	$198.80
Purchase #4	$116.64	12.447%	$131.1582	$131.16	$131.15	$131.20
Purchase #5	$183.36	7.157%	$196.4831	$196.48	$196.50	$196.50
Purchase #6	$52.57	3.218%	$54.2617	$54.26	$54.25	$54.30
Purchase #7	$60.83	5.322%	$64.0674	$64.07	$64.05	$64.10
7 purchase totals =	$776.03		$851.1405	$851.14	$851.15	$851.20