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	$240.39	5.786%	$254.299	$254.30	$254.30	$254.30
Purchase #2	$72.88	9.154%	$79.5514	$79.55	$79.55	$79.60
Purchase #3	$210.80	8.669%	$229.0743	$229.07	$229.05	$229.10
Purchase #4	$179.85	12.371%	$202.0992	$202.10	$202.10	$202.10
Purchase #5	$75.89	6.202%	$80.5967	$80.60	$80.60	$80.60
Purchase #6	$42.73	13.591%	$48.5374	$48.54	$48.55	$48.50
Purchase #7	$85.50	4.534%	$89.3766	$89.38	$89.40	$89.40
7 purchase totals =	$908.04		$983.5346	$983.54	$983.55	$983.60