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	$156.84	9.160%	$171.2065	$171.21	$171.20	$171.20
Purchase #2	$108.43	10.410%	$119.7176	$119.72	$119.70	$119.70
Purchase #3	$100.44	4.235%	$104.6936	$104.69	$104.70	$104.70
Purchase #4	$96.98	8.711%	$105.4279	$105.43	$105.45	$105.40
Purchase #5	$154.95	12.853%	$174.8657	$174.87	$174.85	$174.90
Purchase #6	$20.76	5.713%	$21.946	$21.95	$21.95	$21.90
Purchase #7	$113.41	12.701%	$127.8142	$127.81	$127.80	$127.80
7 purchase totals =	$751.81		$825.6715	$825.68	$825.65	$825.60