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	$194.68	10.514%	$215.1487	$215.15	$215.15	$215.10
Purchase #2	$205.73	10.598%	$227.5333	$227.53	$227.55	$227.50
Purchase #3	$167.44	8.252%	$181.2571	$181.26	$181.25	$181.30
Purchase #4	$175.83	3.126%	$181.3264	$181.33	$181.35	$181.30
Purchase #5	$83.65	4.292%	$87.2403	$87.24	$87.25	$87.20
Purchase #6	$122.35	4.527%	$127.8888	$127.89	$127.90	$127.90
Purchase #7	$234.33	10.764%	$259.5533	$259.55	$259.55	$259.60
7 purchase totals =	$1,184.01		$1,279.9479	$1,279.95	$1,280.00	$1,279.90