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	$140.72	9.753%	$154.4444	$154.44	$154.45	$154.40
Purchase #2	$38.85	3.138%	$40.0691	$40.07	$40.05	$40.10
Purchase #3	$172.68	3.268%	$178.3232	$178.32	$178.30	$178.30
Purchase #4	$148.76	11.332%	$165.6175	$165.62	$165.60	$165.60
Purchase #5	$137.45	7.378%	$147.5911	$147.59	$147.60	$147.60
Purchase #6	$46.71	9.697%	$51.2395	$51.24	$51.25	$51.20
Purchase #7	$55.89	11.708%	$62.4336	$62.43	$62.45	$62.40
7 purchase totals =	$741.06		$799.7184	$799.71	$799.70	$799.60