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	$176.34	12.612%	$198.58	$198.58	$198.60	$198.60
Purchase #2	$216.69	3.749%	$224.8137	$224.81	$224.80	$224.80
Purchase #3	$19.95	5.725%	$21.0921	$21.09	$21.10	$21.10
Purchase #4	$30.80	3.192%	$31.7831	$31.78	$31.80	$31.80
Purchase #5	$55.43	10.705%	$61.3638	$61.36	$61.35	$61.40
Purchase #6	$32.30	9.495%	$35.3669	$35.37	$35.35	$35.40
Purchase #7	$122.63	4.219%	$127.8038	$127.80	$127.80	$127.80
7 purchase totals =	$654.14		$700.8034	$700.79	$700.80	$700.90