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	$137.56	13.783%	$156.5199	$156.52	$156.50	$156.50
Purchase #2	$84.47	5.665%	$89.2552	$89.26	$89.25	$89.30
Purchase #3	$191.31	6.509%	$203.7624	$203.76	$203.75	$203.80
Purchase #4	$71.35	11.132%	$79.2927	$79.29	$79.30	$79.30
Purchase #5	$91.43	12.545%	$102.8999	$102.90	$102.90	$102.90
Purchase #6	$119.57	9.598%	$131.0463	$131.05	$131.05	$131.00
Purchase #7	$162.71	6.552%	$173.3708	$173.37	$173.35	$173.40
7 purchase totals =	$858.40		$936.1472	$936.15	$936.10	$936.20