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	$28.26	12.684%	$31.8445	$31.84	$31.85	$31.80
Purchase #2	$119.31	10.450%	$131.7779	$131.78	$131.80	$131.80
Purchase #3	$111.61	10.276%	$123.079	$123.08	$123.10	$123.10
Purchase #4	$75.99	11.314%	$84.5875	$84.59	$84.60	$84.60
Purchase #5	$80.81	5.415%	$85.1859	$85.19	$85.20	$85.20
Purchase #6	$25.25	11.332%	$28.1113	$28.11	$28.10	$28.10
Purchase #7	$121.34	13.584%	$137.8228	$137.82	$137.80	$137.80
7 purchase totals =	$562.57		$622.4089	$622.41	$622.45	$622.40