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	$70.72	11.164%	$78.6152	$78.62	$78.60	$78.60
Purchase #2	$162.94	7.240%	$174.7369	$174.74	$174.75	$174.70
Purchase #3	$95.58	5.541%	$100.8761	$100.88	$100.90	$100.90
Purchase #4	$198.30	8.159%	$214.4793	$214.48	$214.50	$214.50
Purchase #5	$64.93	11.535%	$72.4197	$72.42	$72.40	$72.40
Purchase #6	$41.54	4.379%	$43.359	$43.36	$43.35	$43.40
Purchase #7	$34.71	11.191%	$38.5944	$38.59	$38.60	$38.60
7 purchase totals =	$668.72		$723.0806	$723.09	$723.10	$723.10