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	$101.58	3.200%	$104.8306	$104.83	$104.85	$104.80
Purchase #2	$51.27	12.221%	$57.5357	$57.54	$57.55	$57.50
Purchase #3	$231.97	9.375%	$253.7172	$253.72	$253.70	$253.70
Purchase #4	$192.67	11.183%	$214.2163	$214.22	$214.20	$214.20
Purchase #5	$196.63	12.789%	$221.777	$221.78	$221.80	$221.80
Purchase #6	$182.81	7.301%	$196.157	$196.16	$196.15	$196.20
Purchase #7	$95.26	8.395%	$103.2571	$103.26	$103.25	$103.30
7 purchase totals =	$1,052.19		$1,151.4909	$1,151.51	$1,151.50	$1,151.50