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	$229.37	11.560%	$255.8852	$255.89	$255.90	$255.90
Purchase #2	$158.76	9.373%	$173.6406	$173.64	$173.65	$173.60
Purchase #3	$234.30	7.102%	$250.94	$250.94	$250.95	$250.90
Purchase #4	$123.69	12.447%	$139.0857	$139.09	$139.10	$139.10
Purchase #5	$238.78	11.230%	$265.595	$265.60	$265.60	$265.60
Purchase #6	$223.75	11.490%	$249.4589	$249.46	$249.45	$249.50
Purchase #7	$10.66	6.609%	$11.3645	$11.36	$11.35	$11.40
7 purchase totals =	$1,219.31		$1,345.9699	$1,345.98	$1,346.00	$1,346.00