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	$52.25	5.523%	$55.1358	$55.14	$55.15	$55.10
Purchase #2	$97.80	12.560%	$110.0837	$110.08	$110.10	$110.10
Purchase #3	$42.75	6.483%	$45.5215	$45.52	$45.50	$45.50
Purchase #4	$250.47	3.842%	$260.0931	$260.09	$260.10	$260.10
Purchase #5	$222.32	6.444%	$236.6463	$236.65	$236.65	$236.60
Purchase #6	$38.81	4.739%	$40.6492	$40.65	$40.65	$40.60
Purchase #7	$37.70	10.308%	$41.5861	$41.59	$41.60	$41.60
7 purchase totals =	$742.10		$789.7157	$789.72	$789.75	$789.60