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	$41.66	13.338%	$47.2166	$47.22	$47.20	$47.20
Purchase #2	$155.83	10.711%	$172.521	$172.52	$172.50	$172.50
Purchase #3	$138.28	3.823%	$143.5664	$143.57	$143.55	$143.60
Purchase #4	$128.53	4.159%	$133.8756	$133.88	$133.90	$133.90
Purchase #5	$114.37	11.234%	$127.2183	$127.22	$127.20	$127.20
Purchase #6	$234.74	10.228%	$258.7492	$258.75	$258.75	$258.70
Purchase #7	$59.72	12.620%	$67.2567	$67.26	$67.25	$67.30
7 purchase totals =	$873.13		$950.4038	$950.42	$950.35	$950.40