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	$140.64	13.415%	$159.5069	$159.51	$159.50	$159.50
Purchase #2	$70.56	12.606%	$79.4548	$79.45	$79.45	$79.50
Purchase #3	$72.52	8.116%	$78.4057	$78.41	$78.40	$78.40
Purchase #4	$212.32	12.486%	$238.8303	$238.83	$238.85	$238.80
Purchase #5	$207.36	12.144%	$232.5418	$232.54	$232.55	$232.50
Purchase #6	$35.80	3.500%	$37.053	$37.05	$37.05	$37.10
Purchase #7	$49.94	4.241%	$52.058	$52.06	$52.05	$52.10
7 purchase totals =	$789.14		$877.8505	$877.85	$877.85	$877.90