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	$45.89	7.695%	$49.4212	$49.42	$49.40	$49.40
Purchase #2	$113.79	5.721%	$120.2999	$120.30	$120.30	$120.30
Purchase #3	$128.91	8.395%	$139.732	$139.73	$139.75	$139.70
Purchase #4	$228.92	11.657%	$255.6052	$255.61	$255.60	$255.60
Purchase #5	$21.84	4.865%	$22.9025	$22.90	$22.90	$22.90
Purchase #6	$183.27	7.238%	$196.5351	$196.54	$196.55	$196.50
Purchase #7	$23.45	9.719%	$25.7291	$25.73	$25.75	$25.70
7 purchase totals =	$746.07		$810.2250	$810.23	$810.25	$810.10