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	$241.32	8.206%	$261.1227	$261.12	$261.10	$261.10
Purchase #2	$205.27	6.331%	$218.2656	$218.27	$218.25	$218.30
Purchase #3	$101.88	9.644%	$111.7053	$111.71	$111.70	$111.70
Purchase #4	$43.62	11.310%	$48.5534	$48.55	$48.55	$48.60
Purchase #5	$36.42	9.757%	$39.9735	$39.97	$39.95	$40.00
Purchase #6	$195.29	13.704%	$222.0525	$222.05	$222.05	$222.10
Purchase #7	$50.27	10.538%	$55.5675	$55.57	$55.55	$55.60
7 purchase totals =	$874.07		$957.2405	$957.24	$957.15	$957.40