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	$24.75	11.316%	$27.5507	$27.55	$27.55	$27.60
Purchase #2	$72.29	8.622%	$78.5228	$78.52	$78.50	$78.50
Purchase #3	$146.87	12.740%	$165.5812	$165.58	$165.60	$165.60
Purchase #4	$195.93	12.359%	$220.145	$220.15	$220.15	$220.10
Purchase #5	$51.26	5.399%	$54.0275	$54.03	$54.05	$54.00
Purchase #6	$36.44	5.295%	$38.3695	$38.37	$38.35	$38.40
Purchase #7	$178.64	6.824%	$190.8304	$190.83	$190.85	$190.80
7 purchase totals =	$706.18		$775.0271	$775.03	$775.05	$775.00