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	$97.29	10.298%	$107.3089	$107.31	$107.30	$107.30
Purchase #2	$57.45	13.337%	$65.1121	$65.11	$65.10	$65.10
Purchase #3	$232.92	12.727%	$262.5637	$262.56	$262.55	$262.60
Purchase #4	$216.84	11.538%	$241.859	$241.86	$241.85	$241.90
Purchase #5	$136.53	6.124%	$144.8911	$144.89	$144.90	$144.90
Purchase #6	$71.60	9.776%	$78.5996	$78.60	$78.60	$78.60
Purchase #7	$227.30	10.383%	$250.9006	$250.90	$250.90	$250.90
7 purchase totals =	$1,039.93		$1,151.2350	$1,151.23	$1,151.20	$1,151.30