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	$180.70	3.268%	$186.6053	$186.61	$186.60	$186.60
Purchase #2	$128.87	6.406%	$137.1254	$137.13	$137.15	$137.10
Purchase #3	$111.95	6.635%	$119.3779	$119.38	$119.40	$119.40
Purchase #4	$182.88	10.123%	$201.3929	$201.39	$201.40	$201.40
Purchase #5	$63.60	11.463%	$70.8905	$70.89	$70.90	$70.90
Purchase #6	$73.91	6.732%	$78.8856	$78.89	$78.90	$78.90
Purchase #7	$165.41	11.194%	$183.926	$183.93	$183.95	$183.90
7 purchase totals =	$907.32		$978.2036	$978.22	$978.30	$978.20