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	$38.35	9.765%	$42.0949	$42.09	$42.10	$42.10
Purchase #2	$22.98	12.734%	$25.9063	$25.91	$25.90	$25.90
Purchase #3	$85.99	4.314%	$89.6996	$89.70	$89.70	$89.70
Purchase #4	$43.73	3.199%	$45.1289	$45.13	$45.15	$45.10
Purchase #5	$184.82	8.433%	$200.4059	$200.41	$200.40	$200.40
Purchase #6	$15.37	13.688%	$17.4738	$17.47	$17.45	$17.50
Purchase #7	$161.88	7.562%	$174.1214	$174.12	$174.10	$174.10
7 purchase totals =	$553.12		$594.8308	$594.83	$594.80	$594.80