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	$131.96	9.339%	$144.2837	$144.28	$144.30	$144.30
Purchase #2	$239.82	9.585%	$262.8067	$262.81	$262.80	$262.80
Purchase #3	$75.87	13.544%	$86.1458	$86.15	$86.15	$86.10
Purchase #4	$166.25	10.152%	$183.1277	$183.13	$183.15	$183.10
Purchase #5	$39.50	8.305%	$42.7805	$42.78	$42.80	$42.80
Purchase #6	$235.90	8.433%	$255.7934	$255.79	$255.80	$255.80
Purchase #7	$94.91	10.815%	$105.1745	$105.17	$105.15	$105.20
7 purchase totals =	$984.21		$1,080.1123	$1,080.11	$1,080.15	$1,080.10