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	$53.67	3.448%	$55.5205	$55.52	$55.50	$55.50
Purchase #2	$223.43	6.866%	$238.7707	$238.77	$238.75	$238.80
Purchase #3	$49.88	6.759%	$53.2514	$53.25	$53.25	$53.30
Purchase #4	$220.71	13.737%	$251.0289	$251.03	$251.05	$251.00
Purchase #5	$76.50	5.136%	$80.429	$80.43	$80.45	$80.40
Purchase #6	$156.59	7.168%	$167.8144	$167.81	$167.80	$167.80
Purchase #7	$143.70	12.784%	$162.0706	$162.07	$162.05	$162.10
7 purchase totals =	$924.48		$1,008.8855	$1,008.88	$1,008.85	$1,008.90