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	$52.33	3.795%	$54.3159	$54.32	$54.30	$54.30
Purchase #2	$184.41	11.617%	$205.8329	$205.83	$205.85	$205.80
Purchase #3	$208.70	10.795%	$231.2292	$231.23	$231.25	$231.20
Purchase #4	$20.64	4.791%	$21.6289	$21.63	$21.65	$21.60
Purchase #5	$10.34	4.167%	$10.7709	$10.77	$10.75	$10.80
Purchase #6	$55.82	5.585%	$58.9375	$58.94	$58.95	$58.90
Purchase #7	$35.40	5.677%	$37.4097	$37.41	$37.40	$37.40
7 purchase totals =	$567.64		$620.1250	$620.13	$620.15	$620.00