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	$51.43	11.213%	$57.1968	$57.20	$57.20	$57.20
Purchase #2	$145.80	9.265%	$159.3084	$159.31	$159.30	$159.30
Purchase #3	$18.37	12.324%	$20.6339	$20.63	$20.65	$20.60
Purchase #4	$90.33	11.396%	$100.624	$100.62	$100.60	$100.60
Purchase #5	$79.53	12.547%	$89.5086	$89.51	$89.50	$89.50
Purchase #6	$174.54	13.321%	$197.7905	$197.79	$197.80	$197.80
Purchase #7	$104.39	7.512%	$112.2318	$112.23	$112.25	$112.20
7 purchase totals =	$664.39		$737.2940	$737.29	$737.30	$737.20