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	$182.82	6.249%	$194.2444	$194.24	$194.25	$194.20
Purchase #2	$127.94	9.686%	$140.3323	$140.33	$140.35	$140.30
Purchase #3	$178.72	12.235%	$200.5864	$200.59	$200.60	$200.60
Purchase #4	$112.36	5.494%	$118.5331	$118.53	$118.55	$118.50
Purchase #5	$95.40	13.229%	$108.0205	$108.02	$108.00	$108.00
Purchase #6	$55.72	4.620%	$58.2943	$58.29	$58.30	$58.30
Purchase #7	$103.29	12.606%	$116.3107	$116.31	$116.30	$116.30
7 purchase totals =	$856.25		$936.3217	$936.31	$936.35	$936.20