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	$191.96	7.709%	$206.7582	$206.76	$206.75	$206.80
Purchase #2	$173.49	3.426%	$179.4338	$179.43	$179.45	$179.40
Purchase #3	$126.35	9.231%	$138.0134	$138.01	$138.00	$138.00
Purchase #4	$206.80	9.803%	$227.0726	$227.07	$227.05	$227.10
Purchase #5	$83.53	6.648%	$89.0831	$89.08	$89.10	$89.10
Purchase #6	$40.55	5.833%	$42.9153	$42.92	$42.90	$42.90
Purchase #7	$165.81	13.587%	$188.3386	$188.34	$188.35	$188.30
7 purchase totals =	$988.49		$1,071.6150	$1,071.61	$1,071.60	$1,071.60