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	$110.79	11.487%	$123.5164	$123.52	$123.50	$123.50
Purchase #2	$135.65	8.726%	$147.4868	$147.49	$147.50	$147.50
Purchase #3	$233.90	11.104%	$259.8723	$259.87	$259.85	$259.90
Purchase #4	$165.31	12.755%	$186.3953	$186.40	$186.40	$186.40
Purchase #5	$119.94	6.139%	$127.3031	$127.30	$127.30	$127.30
Purchase #6	$133.49	10.798%	$147.9043	$147.90	$147.90	$147.90
Purchase #7	$121.77	5.247%	$128.1593	$128.16	$128.15	$128.20
7 purchase totals =	$1,020.85		$1,120.6375	$1,120.64	$1,120.60	$1,120.70