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	$65.90	7.156%	$70.6158	$70.62	$70.60	$70.60
Purchase #2	$148.35	11.310%	$165.1284	$165.13	$165.15	$165.10
Purchase #3	$232.53	11.617%	$259.543	$259.54	$259.55	$259.50
Purchase #4	$75.67	8.141%	$81.8303	$81.83	$81.85	$81.80
Purchase #5	$157.97	8.476%	$171.3595	$171.36	$171.35	$171.40
Purchase #6	$233.35	9.478%	$255.4669	$255.47	$255.45	$255.50
Purchase #7	$123.65	10.164%	$136.2178	$136.22	$136.20	$136.20
7 purchase totals =	$1,037.42		$1,140.1617	$1,140.17	$1,140.15	$1,140.10