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	$117.75	11.847%	$131.6998	$131.70	$131.70	$131.70
Purchase #2	$105.42	8.318%	$114.1888	$114.19	$114.20	$114.20
Purchase #3	$173.25	5.257%	$182.3578	$182.36	$182.35	$182.40
Purchase #4	$80.90	11.649%	$90.324	$90.32	$90.30	$90.30
Purchase #5	$104.94	7.246%	$112.544	$112.54	$112.55	$112.50
Purchase #6	$154.79	9.358%	$169.2752	$169.28	$169.30	$169.30
Purchase #7	$63.54	13.478%	$72.1039	$72.10	$72.10	$72.10
7 purchase totals =	$800.59		$872.4935	$872.49	$872.50	$872.50