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	$36.93	5.594%	$38.9959	$39.00	$39.00	$39.00
Purchase #2	$34.96	10.218%	$38.5322	$38.53	$38.55	$38.50
Purchase #3	$177.67	6.637%	$189.462	$189.46	$189.45	$189.50
Purchase #4	$175.94	5.190%	$185.0713	$185.07	$185.05	$185.10
Purchase #5	$182.31	4.853%	$191.1575	$191.16	$191.15	$191.20
Purchase #6	$6.30	8.481%	$6.8343	$6.83	$6.85	$6.80
Purchase #7	$39.38	7.468%	$42.3209	$42.32	$42.30	$42.30
7 purchase totals =	$653.49		$692.3741	$692.37	$692.35	$692.40