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	$89.88	11.852%	$100.5326	$100.53	$100.55	$100.50
Purchase #2	$205.27	5.516%	$216.5927	$216.59	$216.60	$216.60
Purchase #3	$85.33	7.828%	$92.0096	$92.01	$92.00	$92.00
Purchase #4	$241.77	5.299%	$254.5814	$254.58	$254.60	$254.60
Purchase #5	$152.43	4.211%	$158.8488	$158.85	$158.85	$158.80
Purchase #6	$110.36	6.755%	$117.8148	$117.81	$117.80	$117.80
Purchase #7	$36.58	5.829%	$38.7122	$38.71	$38.70	$38.70
7 purchase totals =	$921.62		$979.0921	$979.08	$979.10	$979.00