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	$159.91	3.833%	$166.0394	$166.04	$166.05	$166.00
Purchase #2	$217.26	9.781%	$238.5102	$238.51	$238.50	$238.50
Purchase #3	$17.61	3.444%	$18.2165	$18.22	$18.20	$18.20
Purchase #4	$137.81	6.310%	$146.5058	$146.51	$146.50	$146.50
Purchase #5	$198.81	4.212%	$207.1839	$207.18	$207.20	$207.20
Purchase #6	$143.51	3.502%	$148.5357	$148.54	$148.55	$148.50
Purchase #7	$176.36	12.604%	$198.5884	$198.59	$198.60	$198.60
7 purchase totals =	$1,051.27		$1,123.5799	$1,123.59	$1,123.60	$1,123.50