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	$74.87	11.106%	$83.1851	$83.19	$83.20	$83.20
Purchase #2	$61.76	12.482%	$69.4689	$69.47	$69.45	$69.50
Purchase #3	$101.55	10.172%	$111.8797	$111.88	$111.90	$111.90
Purchase #4	$167.60	6.711%	$178.8476	$178.85	$178.85	$178.80
Purchase #5	$22.40	4.842%	$23.4846	$23.48	$23.50	$23.50
Purchase #6	$73.72	10.679%	$81.5926	$81.59	$81.60	$81.60
Purchase #7	$9.69	13.261%	$10.975	$10.98	$11.00	$11.00
7 purchase totals =	$511.59		$559.4335	$559.44	$559.50	$559.50