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	$66.97	7.788%	$72.1856	$72.19	$72.20	$72.20
Purchase #2	$223.85	5.684%	$236.5736	$236.57	$236.55	$236.60
Purchase #3	$104.42	13.389%	$118.4008	$118.40	$118.40	$118.40
Purchase #4	$143.82	13.238%	$162.8589	$162.86	$162.85	$162.90
Purchase #5	$173.33	3.744%	$179.8195	$179.82	$179.80	$179.80
Purchase #6	$93.48	10.418%	$103.2187	$103.22	$103.20	$103.20
Purchase #7	$178.25	11.141%	$198.1088	$198.11	$198.10	$198.10
7 purchase totals =	$984.12		$1,071.1659	$1,071.17	$1,071.10	$1,071.20