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	$39.39	9.495%	$43.1301	$43.13	$43.15	$43.10
Purchase #2	$91.44	9.849%	$100.4459	$100.45	$100.45	$100.40
Purchase #3	$19.47	4.564%	$20.3586	$20.36	$20.35	$20.40
Purchase #4	$131.75	8.422%	$142.846	$142.85	$142.85	$142.80
Purchase #5	$83.97	10.251%	$92.5778	$92.58	$92.60	$92.60
Purchase #6	$159.90	9.184%	$174.5852	$174.59	$174.60	$174.60
Purchase #7	$236.74	7.586%	$254.6991	$254.70	$254.70	$254.70
7 purchase totals =	$762.66		$828.6427	$828.66	$828.70	$828.60