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	$116.95	5.368%	$123.2279	$123.23	$123.25	$123.20
Purchase #2	$238.51	8.821%	$259.549	$259.55	$259.55	$259.50
Purchase #3	$112.73	13.537%	$127.9903	$127.99	$128.00	$128.00
Purchase #4	$39.79	11.694%	$44.443	$44.44	$44.45	$44.40
Purchase #5	$80.28	6.522%	$85.5159	$85.52	$85.50	$85.50
Purchase #6	$52.44	4.668%	$54.8879	$54.89	$54.90	$54.90
Purchase #7	$179.35	9.869%	$197.0501	$197.05	$197.05	$197.10
7 purchase totals =	$820.05		$892.6641	$892.67	$892.70	$892.60