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	$28.98	11.329%	$32.2631	$32.26	$32.25	$32.30
Purchase #2	$217.68	5.462%	$229.5697	$229.57	$229.55	$229.60
Purchase #3	$150.98	7.587%	$162.4349	$162.43	$162.45	$162.40
Purchase #4	$80.27	11.234%	$89.2875	$89.29	$89.30	$89.30
Purchase #5	$11.27	4.284%	$11.7528	$11.75	$11.75	$11.80
Purchase #6	$62.64	5.246%	$65.9261	$65.93	$65.95	$65.90
Purchase #7	$47.34	10.131%	$52.136	$52.14	$52.15	$52.10
7 purchase totals =	$599.16		$643.3701	$643.37	$643.40	$643.40