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	$53.55	8.851%	$58.2897	$58.29	$58.30	$58.30
Purchase #2	$242.25	13.472%	$274.8859	$274.89	$274.90	$274.90
Purchase #3	$145.56	3.406%	$150.5178	$150.52	$150.50	$150.50
Purchase #4	$132.59	8.455%	$143.8005	$143.80	$143.80	$143.80
Purchase #5	$127.70	6.668%	$136.215	$136.22	$136.20	$136.20
Purchase #6	$108.59	5.358%	$114.4083	$114.41	$114.40	$114.40
Purchase #7	$135.68	5.578%	$143.2482	$143.25	$143.25	$143.20
7 purchase totals =	$945.92		$1,021.3654	$1,021.38	$1,021.35	$1,021.30