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	$166.42	7.183%	$178.3739	$178.37	$178.35	$178.40
Purchase #2	$35.34	3.320%	$36.5133	$36.51	$36.50	$36.50
Purchase #3	$182.75	8.725%	$198.6949	$198.69	$198.70	$198.70
Purchase #4	$52.35	6.664%	$55.8386	$55.84	$55.85	$55.80
Purchase #5	$77.86	10.222%	$85.8188	$85.82	$85.80	$85.80
Purchase #6	$30.29	6.464%	$32.2479	$32.25	$32.25	$32.20
Purchase #7	$88.36	13.691%	$100.4574	$100.46	$100.45	$100.50
7 purchase totals =	$633.37		$687.9448	$687.94	$687.90	$687.90