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	$53.49	4.656%	$55.9805	$55.98	$56.00	$56.00
Purchase #2	$129.34	6.311%	$137.5026	$137.50	$137.50	$137.50
Purchase #3	$45.65	11.596%	$50.9436	$50.94	$50.95	$50.90
Purchase #4	$8.73	9.636%	$9.5712	$9.57	$9.55	$9.60
Purchase #5	$40.65	5.539%	$42.9016	$42.90	$42.90	$42.90
Purchase #6	$128.84	8.135%	$139.3211	$139.32	$139.30	$139.30
Purchase #7	$59.67	10.130%	$65.7146	$65.71	$65.70	$65.70
7 purchase totals =	$466.37		$501.9352	$501.92	$501.90	$501.90