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	$28.64	8.859%	$31.1772	$31.18	$31.20	$31.20
Purchase #2	$226.73	10.382%	$250.2691	$250.27	$250.25	$250.30
Purchase #3	$5.27	11.234%	$5.862	$5.86	$5.85	$5.90
Purchase #4	$127.29	11.739%	$142.2326	$142.23	$142.25	$142.20
Purchase #5	$110.67	11.452%	$123.3439	$123.34	$123.35	$123.30
Purchase #6	$163.47	12.280%	$183.5441	$183.54	$183.55	$183.50
Purchase #7	$10.65	13.474%	$12.085	$12.09	$12.10	$12.10
7 purchase totals =	$672.72		$748.5139	$748.51	$748.55	$748.50